Huberman Lab - Effects of Fasting & Time Restricted Eating on Fat Loss & Health

Welcome to the Huberman Lab Podcast,

where we discuss science

and science-based tools for everyday life.

I’m Andrew Huberman,

and I’m a professor of neurobiology and ophthalmology

at Stanford School of Medicine.

Today, we’re talking all about fasting.

And anytime we’re talking about fasting,

we are also talking about eating

because we all need to eat sooner or later.

We’re going to talk about how fasting

and when we eat influences a large range of aspects

of our health and wellbeing, both physical and mental.

So while nowadays,

most people are familiar with the term intermittent fasting,

also sometimes called time-restricted feeding,

I think most people don’t really understand

how that process works.

It’s sort of obvious that intermittent fasting,

aka time-restricted feeding,

involves eating at certain periods of each 24-hour cycle,

or maybe even not eating for entire days in some cases.

But if you think about it, everybody sleeps eventually,

and therefore, because people don’t eat during their sleep,

almost everybody is employing some form

of intermittent fasting or time-restricted feeding.

What we’re going to talk about today

is how particular schedules of time-restricted feeding

can impact our health in different ways.

And when I say different ways,

I mean, we’re going to talk about

how intermittent fasting, aka time-restricted feeding,

impacts weight loss, fat loss in particular,

muscle maintenance and loss and gain,

organ health, such as gut health and liver health,

the genome, the epigenome, inflammation,

sickness, recovery, and healing from sickness,

exercise, cognition, mood, and lifespan.

So we’re going to cover a tremendous amount of information.

I promise to make it all directly accessible,

regardless of whether or not you have a background

in biology and metabolic science or not.

I’m also going to talk about a lot of tools.

In fact, I’m going to discuss a number of tools

during today’s episode that actually make it such

that you don’t have to follow any feeding schedule

or fasting schedule, same thing, if you think about it,

in any absolutely strict regimented way,

meaning if you were to only eat during an eight hour

period of each day, most of the time,

but then occasionally eat across a 12 hour period

of the day, in theory, that could actually have

pretty serious detrimental health effects.

And yet there are things that you can do

to attenuate those negative effects.

In fact, there are things that you can do and or take

that can make it as if you did not eat at all.

And so we’ll discuss what those tools are.

And in many cases, for sake of health, weight loss

and performance, making the body think that it did not eat

at all can actually be quite beneficial.

Today, we’re going to cover mechanism

and we’re going to cover tools.

Before we do that, I want to highlight a particular result

that was published recently because it serves

as a useful backbone as we wade into the conversation

about fasting.

This is a study that was published

in the journal Cell Metabolism, a cell press journal,

excellent journal.

And the title of the paper is fasting blood glucose

as a predictor of mortality, lost in translation.

And I’ll explain what the lost in translation part means

in a moment.

But the basic takeaway of this study,

and I should mention that the first author of the study

is Paliyaguru, P-A-L-I-Y-A-G-U-R-U, guru,

Paliyaguru et al.

The basic finding of the study is that in humans,

higher blood glucose is associated with mortality.

And in fact, if you look at blood glucose,

resting blood glucose across the lifespan,

what you find is as people age,

resting blood glucose goes up.

Now this is very interesting because for a long time,

it was thought that metabolism actually goes down

as we age.

And to some extent that’s true,

but the reductions in metabolism are not nearly as robust

as we once thought that they were across the lifespan.

However, unless there’s something done to mitigate

the increase in blood glucose associated with the aging,

almost everybody experiences a gradual,

but regular increase in resting blood glucose

that predicts mortality.

Now, the title, as I mentioned,

is fasting blood glucose as a predictor of mortality,

lost in translation.

And the reason that they included lost in translation

in the title is that what I just told you

that increases in resting blood glucose predict mortality

or are correlated with mortality is true for human beings

and for non-human primates, monkeys,

but the opposite is true in mice.

And so I thought it was important to use this study

as an example of where studies in mice often,

but not always translate to humans and to non-human primates.

So today I’m going to be careful to distinguish

when a study was performed in mice versus in humans,

because it seems that at least when discussing

feeding blood glucose and other aspects of diet,

as they relate to health and wellbeing,

whether or not a study was performed in rodents

or in humans can be very important.

In this case,

the results were directly 180 degrees

opposite to one another.

In other words, in mice,

resting blood glucose went down

and it was associated with mortality.

So lower blood glucose associated with mortality,

whereas in humans,

higher resting blood glucose was associated with mortality.

And obviously what we’re mostly interested in

is health and wellbeing of ourselves, of humans.

I’m sure there are some people out there

that are intensely concerned about the health

and wellbeing of mice,

which you could imagine a few rare contexts

where that’s important,

but obviously most of us are interested in human health.

So I’ll be sure to emphasize when studies were performed

in humans versus in mice.

Before we begin,

I’d like to emphasize that this podcast is separate

from my teaching and research roles at Stanford.

It is however,

part of my desire and effort to bring zero cost

to consumer information about science

and science related tools to the general public.

In keeping with that theme,

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Okay, so let’s talk about feeding,

fasting, health, and performance.

And I want to just establish a few foundational terms

so that we’re all on the same page.

First of all, rather than talk about fasting

or time-restricted feeding,

I’m largely going to talk about time-restricted feeding,

but please understand that time-restricted feeding

is just one side of the coin that is a two-sided coin

that includes fasting on the one hand, not eating,

and time-restricted feeding on the other hand.

I may occasionally say fasting,

but because fasting and eating

establish different biological conditions in the body,

time-restricted feeding is the term that I will use

to describe the overall plan

of restricting one’s eating window, as it’s called,

to a particular phase of each 24-hour day,

or in some cases, to particular days within the week,

because as you’ll soon learn,

there are aspects of time-restricted feeding, aka fasting,

that involve eating every other day

or eating one way for five days

and then fasting for two days and so forth.

So I’ll be very precise about what I mean and why I mean it,

but for the time being,

I’m going to refer to time-restricted feeding

as a way to put an umbrella over this conversation.

Second of all,

I am going to emphasize a lot of biological mechanism.

If you’ve listened to this podcast before,

you know that I always begin with biological mechanism.

I do describe tools of how to implement those mechanisms,

but I wholeheartedly believe that knowing mechanisms

and understanding how these processes work

gives you tremendous flexibility and understanding

and control over the processes

of your mental and physical health.

Whereas if I were to just list off a menu of things to do

and not to do, those will work,

but those will not give you the kind of understanding

that would allow you to navigate through life,

through travel, through dinners out,

through different exercise schedules,

whether or not you’re one age or another age,

male, female, et cetera.

I’m giving you mechanisms so that you can gain more control

over the systems in your brain and body.

Everything’s timestamped,

so if you want to jump to the to-dos,

you can certainly do that,

but I encourage you to hang in there for the mechanism bit.

I will make it all very clear

because if you understand mechanism,

you are in a true place of power and control

over your biology.

If ever there was a topic that is controversial,

especially on the internet,

it is that of diet and nutrition.

So I’m wading into this with a smile

and in eager anticipation of all the,

but, but, but this, and but, but that,

and wait, but this showed that.

Here’s the deal.

We need to precisely define what it is

that we’re talking about when we talk about nutrition.

I’m going to give you an example of a study

that was published a few years ago, 2018,

by a colleague of mine at Stanford,

Chris Gardner is a terrific professor of nutrition

and has done a lot of important studies

on how nutrition impacts different aspects of health.

This is a large-scale study.

It was published in JAMA,

the Journal of the American Medical Association,

one of the very top tier journals in the area of medicine.

And certainly for a paper on nutrition to show up there

meant that it had to meet an exceedingly high standard.

This paper where Chris is the first author,

it’s Gardner et al, 2018, JAMA,

looked at weight loss in people following

one particular diet versus another particular diet.

And this was a 12 month weight loss study.

So it was focused specifically on weight loss,

although they looked at some other parameters as well.

And the basic conclusion of the study

was that there was no significant difference

in weight change between people following

a healthy low-fat diet

versus a healthy low-carbohydrate diet

with significantly more dietary fats in them.

This caused a lot of ripples in the world of nutrition

and nutritional science,

and certainly in the general population,

because anyone that understands diet and nutrition

would immediately say, but wait,

there are all sorts of different implications

of eating one type of diet,

say low-carbohydrate, higher fats,

versus a higher-carbohydrate, lower-fat diet.

And indeed there are.

This study was focused specifically on fat loss

and on weight loss.

So as we discuss time-restricted feeding,

we need to be very precise about what are the effects

of time-restricted feeding

and of eating in particular ways at particular times.

We are going to emphasize again,

whether or not the study was done in mice or in humans,

in athletes and men and women or both.

But the study from Gardner and colleagues

is a beautiful study and really emphasizes

that if one’s main goal is simply to lose weight,

then it really does not matter what one eats,

provided that the number of calories burned

is higher than the number of calories ingested.

However, anyone out there

who understands a little bit of biology

or a lot of biology will agree

that there are many factors that impact

that calories burned part of the equation.

Some of those are obvious.

So for instance, amount of exercise,

type of exercise, basal metabolic rate,

how much energy one burns just sitting there.

I’ve talked before on this podcast

about NEAT, non-exercise induced thermogenesis,

where if people bounce around a lot and fidget a lot,

they can burn anywhere from 800 to 2000 calories per day.

So their quote unquote basal metabolic rate

is actually much higher simply because they’re fidgeters.

Whereas people who tend to be more stationary

have a lower basal metabolic rate on average.

There’s great science to support this.

Metabolic factors and hormones are also very important.

Hormones such as thyroid hormone and insulin

and growth hormone and the sex steroid hormones,

testosterone and estrogen,

those levels will also profoundly influence

the calories out, the calories burned component

of the calories in calories out equation.

So if out there on the internet

or in listening to a particular podcast or speaker,

somebody says, this is the ideal diet

or calories in calories out does not matter

or calories in calories out is the only thing that matters.

I think it’s very important to understand

that there are some foundational truths

such as calories in calories out,

but that of course hormone factors

and the context in which a given diet regimen

is taking place are exceedingly important.

A good example of this would be puberty.

At that time in life,

sex steroid hormones are changing profoundly in the body

as are growth hormone and other hormones.

And much of caloric intake is directed

towards protein synthesis,

towards the production of muscle and bone

and other tissues of the body.

And that’s because of changes in hormones

that we call puberty.

So there’s no way that we can drill into every aspect

of a given feeding plan or feeding schedule

that would allow us to tap into every aspect

of the list that I read out before,

weight loss, fat loss, muscle, organ, genome, epigenome,

inflammation, exercise, cognition, mood, and lifespan.

But today we’re going to be very precise

about how time-restricted feeding,

it’s very clear from both animal studies and human studies

can have a very powerful and positive impact

on everything from weight loss and fat loss

to various health parameters.

This is a beautiful literature that’s emerged mostly

in the last 10 or 15 years.

And as we march into this literature,

what you’ll see is that there actually is a perfect diet

for you on a given day.

And that perfect diet for you on a given day is contextual,

meaning it depends on what you did yesterday

and what you’re going to do tomorrow.

So there is a perfect diet for you.

And today I’m going to arm you with the mechanisms

and understanding that will allow you to define

what that perfect diet is and will allow you to eat

on a schedule and to eat the things

that are going to best serve your goals.

So let’s talk about eating and what happens when you eat.

And let’s talk about fasting or not eating

and what happens when you fast.

I did an entire episode on eating and metabolism

and hormones and other factors that impact appetite.

We don’t have time to go into all those details now,

although you’re welcome to listen to that episode as well.

But we can briefly describe the overall conditions

that are set in the body when we eat and when we don’t eat.

The key word here is conditions.

If I can emphasize anything today,

it’s that what you eat and when you eat it,

set conditions in your body.

And those conditions can be very good for you

or very bad for you, depending on when you eat.

In fact, when you eat is as important as what you eat.

I’ll repeat that.

When you eat is as important as what you eat,

at least as it relates to health parameters,

in particular liver health and mental health.

Some simple rules about eating.

First of all, when you eat, typically your blood glucose,

your blood sugar will go up.

Also insulin levels will go up.

Insulin is a hormone that’s involved in mobilizing glucose

from the bloodstream.

How much your glucose and insulin go up

depends on what you eat and how much you eat.

In general, simple sugars, including fructose from fruit,

but also sucrose and glucose and simple sugars

will raise your insulin and blood glucose

more than complex carbohydrates,

things like grains and breads and pastas and so forth.

And grains and breads and pastas and so forth

will raise your blood glucose

more than fibrous carbohydrates like lettuce and broccoli

and things of that sort.

Protein has a somewhat moderate or modest impact

on insulin and glucose.

And fat has the lowest impact

on raising your blood glucose and blood insulin.

So what you eat will impact how steep a rise

in blood glucose and insulin takes place.

And there are a number of factors that are related

to your individual health that will also dictate how steep

and how high that rise in glucose and insulin will be.

For the time being,

I’m leaving out people who have type one diabetes.

These are people that don’t manufacture their own insulin.

And type two diabetes is essentially insulin insensitivity,

lack of sensitivity to insulin,

which leads to high blood glucose.

But when you eat, blood glucose goes up.

And when you don’t eat, blood glucose and insulin go down.

The longer it’s been since your last meal,

the lower typically your blood glucose and insulin will be.

And the higher things like GLP-1,

glucagon-like peptide one,

glucagon being a hormone that’s also secreted

when you are in a fasted state

or a low blood glucose state.

It’s involved in mobilizing various energy sources

from the body, including fat

through what we call lipolysis,

also using carbohydrates and potentially even using muscle

as a source of energy.

So that’s kind of a fire hose of information

about what happens when you eat and don’t eat.

But just think of it this way,

blood sugar and insulin go up when you eat,

they go down when you don’t eat

and other hormones go up when you don’t eat.

So there are hormones associated with the fasted state

and there are hormones associated with the eating

and having just eaten state.

Now, the most important thing to understand

is that like everything in biology,

this is a process that takes time.

So insulin and glucose go up when we eat

and it takes some period of time for them to go down.

Even if we stop eating,

they will remain up for some period of time

and then go back down.

It takes time.

This is very important

because if you look at the scientific literature

on fasting, on time-restricted feeding,

it’s absolutely clear that the health benefits,

not just the weight loss benefits,

but that the health benefits from time-restricted feeding

occur because certain conditions are met

in the brain and body for a certain amount of time.

And that gives us an anchor from which

to view what eating is

in terms of how it sets conditions in the body over time.

And if that sounds overly analytic,

I promise you this is the simplest and best way

to think about any eating schedule or any eating plan.

So I think it’s fair to say that in the field of nutrition,

there are a few landmark studies

that serve as really strong anchors

for building our understanding of what to eat

and what not to eat and when to eat,

depending on our goals.

The Garner study that I mentioned earlier

is one such study in that it says,

if your goal is weight loss,

it really does not matter what foods you consume

provided that you consume a sub-maintenance caloric diet.

However, I want to emphasize again,

that sets aside issues of adherence,

meaning how easy or hard it is to adhere to a given diet.

Some people find it much easier

to follow a high-fat, low-carbohydrate diet.

Some people follow a different diet

because it’s much easier for them to follow.

And some people are concerned with mental performance

and athletic performance.

So that study doesn’t say there’s a best diet.

What it says is that what you consume is less important

than the amount of food that you consume,

at least for sake of weight loss,

not necessarily for sake of health.

Now, the study that I’m going to refer to next

is what I would consider the second major pillar

of nutritional studies.

This is a truly landmark study that was carried out

by Sachin Panda, who is a professor

at the Salk Institute of Biological Studies in San Diego,

an absolutely phenomenal institution

and an absolutely phenomenal researcher.

I’ve known Sachin for a number of years,

and I want to emphasize that the current literature

on intermittent fasting and time-restricted feeding

can largely be attributed to Sachin

and the work that he’s done.

There are others involved too, of course,

time-restricted feeding and fasting has a rich history

that goes back many hundreds, if not thousands of years

in different cultures and religions,

but the science of time-restricted feeding

can really mainly be attributed to the incredible work

that Sachin has done.

And I’m grateful to consider him a friend and a colleague.

And we consulted at length in anticipation of this episode.

I also hope to have him on as a guest in the future.

The landmark paper that came from Sachin’s lab

was published in 2012.

This was a paper in mice that set the basis

for studies in humans that came later.

And the title of this paper is

Time-Restricted Feeding Without Reducing Caloric Intake

Prevents Metabolic Diseases in Mice Fed a High-Fat Diet.

So the title tells us a lot.

It says that what’s varied in this study

is not what these mice ate, it was when they ate it.

And there were essentially four conditions in this study

and the results are absolutely remarkable.

So I’m going to walk you through the major results.

What they did is they gave mice access

to different types of food.

There were four groups.

One group of mice had access to just a normal mouse diet.

It would not be a diet that you’d be very interested in.

I confess I’ve actually tasted mouse chow.

If you work with mice at all,

you just have to do it at least once.

It doesn’t taste very good.

It tastes like a very bland graham cracker cookie.

And I confess that I only had the tiniest little bit,

but mice like that stuff.

And if you allow them to eat that stuff,

what’s called ad libitum, whenever they want,

you just keep it in their food 24 hours a day.

They will eat sometimes

and then they won’t eat it at other times.

Or in this case, they also had a condition

where they gave them mouse chow in a time restricted way,

just for a certain number of hours each day

of about eight hours.

Or they gave them a high fat diet.

That was a separate group,

got a high fat diet at any time they wanted.

So this was kind of the carnival for mice

because mice really like high fat,

highly palatable foods.

And so they got a lot of goodies

and high fat in their food.

And then there was a fourth group

that had access to the high fat diet

as much as they wanted to eat,

but only during a restricted time period

of each 24 hour cycle.

Now mice are nocturnal, humans are what we call diurnal.

Actually, we’re not really diurnal, we’re crepuscular,

which means that we’re most active in the morning

and in the evening, not so much in the afternoon.

But nonetheless, everything I’m going to tell you

is true also for humans.

And we know this now from human studies.

One of the most important things to take away

from the study was that mice that ate a highly palatable,

high fat diet, a great tasting diet,

but only during a restricted feeding window

of each 24 hour cycle,

maintained or lost weight over time.

Whereas mice that ingested the same diet,

same amount of calories,

but had access to those calories around the clock,

gained weight, became obese and quite sick.

And as an additional second point,

the mice that restricted their feeding window

to a particular portion of eight hours

of every 24 hour cycle,

actually showed some improvement

in important health markers.

And what was even more incredible is that mice

that only ate during a particular feeding window

also experienced some reversal

of some prior negative health effects.

So this study really lit up the world

and got people excited about time-restricted eating.

Again, they used an eight hour feeding window.

The story around that eight hour feeding window

is kind of interesting though.

Not many people know this

because it wasn’t included in the paper

and there was no reason to include it in the paper,

not to out anybody,

but it turns out that the reason they used

an eight hour feeding window

and not a nine hour or a 10 hour feeding window

is because studies of this sort

are actually quite demanding to perform

and require the constant presence

of the graduate student or postdoc there

to ensure that the food is in the cages at particular times

and not in the cages at other times.

And mice are really good at hiding food.

They’ll even hide food in their jowls.

And so there’s a lot of work that has to be done

to prepare for that eight hour feeding window

and to make sure after that eight hour feeding window,

there’s all the food has been removed from the cage

and from the jowls of the mice and so forth.

And it turns out that the significant other

of the graduate student and or postdoc,

I won’t reveal who they were running this study,

forbid their significant other, the scientist,

from being in the lab for periods of time

that were much longer than the 10 or 12 hours

that were required in order to ensure

this eight hour feeding window.

So when we hear the eight hour feeding windows are holy,

they are not holy.

And later we are going to talk about how eating

for a time that’s restricted to eight hours

versus 10 hours versus 12 hours, for instance,

how that impacts various parameters like health parameters

and weight loss, et cetera.

But the eight hour feeding window was actually created

because of a real world constraint on the research

and the relationship of the researcher

performing the research,

not because there’s anything holy

about an eight hour feeding window.

Now, an important point about when the feeding window falls

within the 24 hour cycle,

it is very important that the feeding window fall

during the more active phase of one’s day.

So for humans, that’s typically in the early part of the day

or the later part of the day, but not at night.

Put very simply, there are a lot of data now

pointing to the fact that eating during the nocturnal phase

of the 24 hour cycle is very detrimental to one’s health.

In fact, when we eat can either enhance our health

or can diminish our health.

When we see light can enhance our feelings of wellbeing

or can diminish our feelings of wellbeing.

I’ve talked many times before about this

on the Huberman Lab Podcast that during the daytime,

you want to get as much sunlight

and other types of bright light in your eyes

as is safely possible.

And then you want to avoid light in the middle of the night.

It has detrimental dopamine lowering effects,

can cause depression, cortisol increases, et cetera.

So when you view light is as important

as the light that you view.

And when you eat is as important as what you eat.

In this study, they saw something really interesting,

which was that not only did restricting food

to a particular phase of the 24 hour cycle

benefit things like lean body mass and fat loss

and a number of health parameters

that I’ll talk about in a moment,

but it also anchored all the gene systems of the body

and provided a more regular stable

so-called circadian rhythm or 24 hour rhythm.

You may be surprised to learn that 80%,

80% of the genes in your body and brain

are on a 24 hour schedule.

That is they change their levels going from high to low

and back to high again across the 24 hour cycle.

And when those genes are high at the appropriate times

and low at the appropriate times,

meaning their expression is high and low

at the appropriate times,

and therefore the proper RNAs and proteins are made

because DNA encodes for RNA,

RNA is translated into proteins.

When that happens, your health benefits.

When those genes are not expressed at the right times,

when they’re higher or low at the wrong times

of each 24 hour cycle,

that’s when you get negative health effects.

This study showed that when mice restrict their eating

to an eight hour period within the most active phase

of their 24 hour cycle,

many of the genes that are associated

with these so-called circadian and clocks,

these genes have names like PER, BMAL, CRY1, et cetera.

Those so-called clock genes

underwent a very regular entrainment,

a locking in to the proper 24 hour schedule.

And while this was in mice,

we now know that this also occurs in humans.

I’ve said before on this podcast, and I’ll say it again,

that light and when we view light is the primary way

in which these genes and the clock systems of our body

get organized or entrained,

meaning matched to the outside light dark cycle.

So viewing light early in the day and in the afternoon

and as much as possible all day, great.

Ideally that sunlight.

Avoiding light in the middle of the night is also great.

It’s great because it causes the increases

in particular genes and the decreases in particular genes

in every cell throughout your body

at the appropriate times.

The second most powerful timekeeper or Zeitgeber

as it’s called is food and when you eat.

And in this study, the results they saw,

underscore this point,

what they saw is that the peaks in these clock genes

became very regular.

And the dips in these clock genes became very regular.

And that led to a whole host

of really important positive health effects.

Conversely, when mice ate whenever they wanted

across the 24 hour cycle,

these clock genes became really out of whack

and the negative health consequences

were the downstream result of these changes

in these clock genes.

This has now also been shown to be true for humans.

So if you want to be healthy,

you want your organ health,

your metabolic health to be entrained properly.

One of the most important things you can do

is to view light at the appropriate times

of each 24 hour schedule

and to not view light at other times of that schedule

and to eat at the appropriate time of each 24 hour day.

Now, again, there are rare instances that we will discuss

when skipping entire days or entire 24 hour cycles

of eating can be beneficial.

But for now we’re talking about schedules

of time-restricted feeding that involve a window of feeding

that falls during your more active phase.

So during the daytime,

putting aside people that work shift work,

during the daytime is when you want to eat.

And this eight hour feeding window

provided a very strong reinforcing signal

that combines with light to ensure that these genes

are expressed at the appropriate times.

The short takeaway from this

is you probably want to think about

and perhaps even engage in time-restricted feeding.

So as I mentioned earlier,

when mice can eat around the clock, bad things happen.

And one of the bad things that happens

is that the liver suffers.

The liver is involved in all sorts of things,

production of important hormones and other factors

related to metabolism.

And when mice can eat around the clock,

their livers got very sick, fatty deposits in the liver,

other factors in the liver,

essentially taking down the pathway of liver disease.

The time-restricted feeding essentially reversed that

or led in many cases to even healthier liver conditions.

And that’s based on this study,

but also additional studies also now in humans.

So restricting your feeding

to a particular window every 24 hour cycle

has clearly been shown now in mice and in humans

to enhance liver health, which is wonderful.

How does it do this?

Well, it happens because food intake,

as I mentioned earlier,

sets certain conditions in the body

that last for a period of time.

Anytime we eat, whether or not we are a mouse or a human,

there’s a period of time

that’s required for so-called digestion,

but also gastric emptying and other processes

related to breaking down that food and utilizing it.

And that is an active process.

It requires energy.

And that process of breaking down food

involves certain cellular functions

that if they’re ongoing throughout the 24 hour cycle

or even extended too far across the 24 hour cycle,

meaning you’re eating across a 14 or a 16 hour

or an 18 hour window, that causes serious problems.

And this has now been established

because of the fact that it increases the expression

of different proteins and genes in the body,

such as TNF alpha, IL-6, IL-1, what are all those things?

They are pro-inflammatory markers.

So the reason that the liver gets sick

when you’re eating too often

is because inflammatory markers are increased.

These inflammatory markers are not inherently bad.

They’re there for a reason,

but they are there in order to respond

to certain challenges, immune challenges,

or the ingestion of food and the breakdown of food.

But then in an ideal circumstance,

they are reduced in the period

in which there’s no food present in the digestive tract

or in which there’s very little food

present in the digestive tract.

So by eating around the clock,

you’re making yourself sicker.

By eating at restricted periods of time each 24 hour day,

you’re actually making yourself healthier

and you are activating certain processes

that can positively impact both weight,

either maintenance or loss of weight.

We’ll talk about weight gain a little later

and positively impacting things like liver health.

Also the expression of different things

related to brown fat,

the fat that increases your metabolism.

We will return to this also a little bit later

and blood glucose regulation.

So the takeaway from this study,

in fact, there are many takeaways from this study,

it’s so wonderful,

is that liver health, bile acid metabolism,

energy expenditure, inflammation, liver metabolites,

many, many aspects of our health

are impacted by when we eat, not just what we eat.

As we move forward and we talk about intermittent fasting

for eight hour windows, six hour windows, 12 hour windows,

for all sorts of different intents and purposes,

I want to start to establish a foundational protocol

that all of us, any of us can use

in order to maximize your particular goals.

There are some absolutes within this realm

of time-restricted feeding.

Here are a couple of absolutes

that you would want to consider.

First of all, it pays off in the metabolic sense

and in the health sense

and in the weight maintenance or loss sense

to not ingest any food in the first hour after waking

and potentially for longer.

So I want to repeat that.

One of the key pillars of intermittent fasting

is that for the first hour after you wake up

and potentially for longer to not ingest any food, okay?

The second major pillar that’s well-supported by research

is that for the two and ideally three hours

prior to bedtime, you also don’t ingest any food

or liquid calories for that matter.

And we will talk about what it means to break a fast

and whether or not certain liquids,

even coffee and tea can break a fast, et cetera,

in a few moments.

But just as a foundation,

it’s very clear from the research in humans

that not eating any food or ingesting any calories,

liquid or otherwise,

for the first 60 minutes after waking up each day

and for the two to three hours prior to your bedtime,

that’s ideal for the parameters

that we’ve discussed earlier,

all the different things like weight and liver health

and metabolic health and so forth.

The two most common questions about intermittent fasting

are when is the ideal time for the eating window?

Is it early in the day, the middle of the day,

or later in the day?

And how long should that eating window be?

Should it be eight hours?

We already heard why the eight hour window

was first established.

It was because of these lab conditions

and the conditions of the particular relationship

of the graduate student involved,

or should it be seven hours or six hours or 12 hours?

Turns out that there’s some general frameworks

that we can follow in order to answer these questions.

As we move into this portion of the discussion,

I want to highlight a very important reference

that just came out, literally came out last week

in the journal Endocrinology Reviews.

And the title of this review is time-restricted eating

for the prevention and management of metabolic diseases.

Although the data in this paper

go well beyond metabolic diseases.

This is a paper from Sachin Panda’s lab.

It’s a very lengthy review with an enormous table

that’s beautifully organized,

that scripts out all the studies done in humans,

well over a hundred studies,

looking at time-restricted feeding in athletes,

men, women, children, diabetes, no diabetes, et cetera,

with detailed references and description of the outcomes.

Spent a lot of time with this review,

even though it just came out recently,

and is a absolute goldmine resource.

It is also the major resource

for everything I’m about to tell you

if you would like to delve deeper into the material.

So let’s deal with this first question

of when is the ideal feeding window?

And here again, we’re thinking about a schedule of eating

that involves eating at least once every 24 hours,

not two day or three day or every other day fast.

So it turns out that the answer to the question,

when is it best to eat is actually best answered

by thinking about the other side of the coin,

which is when is it best to fast?

So because we are fasting during sleep,

it’s very clear that it’s best to extend

the sleep-related fast either into the morning

or to start it in the evening.

Now this might seem kind of obvious,

but it’s actually not so obvious.

You could place that feeding window early in the day,

middle of the day or late in the day.

Let’s think about what happens when we sleep.

When we sleep, our body undergoes a number

of different processes in the brain and body

in order to recover the cells and tissues.

Many of you have probably heard of autophagy,

which is essentially a cleaning up,

a gobbling up of dead cells

and cells that are injured or sick.

And this is a natural process that occurs

and it occurs mainly during sleep,

although not only during sleep.

Fasting of any kind does tend to enhance autophagy.

It is not the only way to create autophagic conditions.

Autophagic conditions can be created simply

by following a sub caloric diet.

And there are other things that one can do

in order to trigger autophagy,

but fasting does trigger autophagy.

So when we’re asleep,

the bad cells are getting gobbled up and eaten.

And the good cells also are undergoing

certain repair mechanisms mainly related to,

or at least governed by those circadian genes

that we talked about earlier, those clock genes.

So you’re already fasting when you’re asleep

and how deep you are into that fast depends

on how long it was since your last meal.

So if you fast early in the day

and you’ve been asleep for five, six, seven, eight hours,

I would hope somewhere between six and eight hours

for most people is going to be beneficial.

When you wake up, I mentioned earlier

that you don’t want to eat

for at least the first 60 minutes after waking,

but were you to extend that fasting to say 9 a.m., 10 a.m.,

11 a.m. or even 12 noon or later,

you are taking advantage of the deep fast

that you were in during sleep

and certainly toward the end of sleep.

Now, why do I say deep fast?

Well, because when we eat,

the clearance of that food from our gut

and the processes in our cells and organs

that are related to digestion

and the utilization of that food

takes about five to six hours.

So if you eat a meal and that meal lasts 10 minutes,

20 minutes, or 30 minutes, or even an hour,

and then you stop eating, you’ve stopped eating,

but you are not fasting at that point.

You can say you’re fasting

because you’re no longer putting food

into your digestive tract,

but you are not in a fasted state.

You are not under conditions of fasting.

Later, I’ll talk about things that you can do

to accelerate the transition into fasting.

So one thing is certain,

that you want your eating window to be tacked

or attached to your sleep-based fasting

in a way that makes it easier for you

to get into the fasted state for a period of time.

So we can view that point from the perspective

of best, better, and worst, okay?

So if you are like most people and you sleep at night,

you’re waking up somewhere around 6.30, 7 a.m.,

or maybe even 8 a.m.,

let’s say you were to push your fasting window out

such that you started eating at noon,

and then you stopped eating at 6 p.m.

Well, then you’re not eating from 6 p.m.

until let’s say your bedtime is 10 p.m.,

but from 6 p.m. to 10 p.m.,

your body is not yet in a fasted state

because you just ate.

However, you’re starting to taper

into a fasted state before sleep,

and then all through sleep,

and until the next morning and late morning,

you are actually in a fasted state.

Now, most people find it very hard

to only eat in the middle of the day.

So while that’s best, it’s ideal

for sake of the fasting-related improvements in health,

it is not ideal, and it’s not very applicable

to most work and family and social situations.

Most people eat breakfast with others

and or eat dinner with others.

Some people eat lunch with others,

but in general, it’s hard to restrict your feeding window

to just the absolute middle of the day.

But from a purely health perspective,

in a very objective way,

that would be the ideal situation.

Let’s imagine a different pattern of eating

where the feeding window starts in the afternoon,

starts around 2 or even 3 p.m.

Some people don’t have much trouble

or they can train themselves

to get their feeding window out

to 2 or 3 p.m., and then they will eat

until 10 or 11 p.m., right?

If you do the math, you realize

that that feeding window is still pretty short.

It still constitutes what we would call

intermittent fasting or time-restricted feeding.

But assuming that they go to bed

around 11 p.m. or midnight,

they are not actually fasted in sleep

because for the first six hours or so of sleep,

maybe five, but probably more like six hours of sleep,

they’re still digesting the food

that they consumed late in the night.

It does appear beneficial

to grab a hold of that sleep-related fast,

meaning you don’t want your feeding window

to be too close to bedtime.

And that’s why we came up with this

kind of foundational pillar

that I discussed with Sachin earlier,

which is at least no eating for the first hour after waking,

but also no eating within two to three hours prior to bed.

And because we all need to sleep

and sleep is exceedingly important

for our health of all kinds,

you want to prioritize sleep,

but because we also have to eat,

then you start to think about this

and maybe it’s not so good to push that feeding window

too late in the day, because when you go to sleep,

you’re not actually capitalizing

on the sleep-related fasting.

Now, it’s not just the case

that it’s easiest to fast while in sleep,

although that’s true because when we’re asleep,

typically we’re not hungry or looking for food

or foraging for food or wanting food

or trying to resist food.

We’re just sleeping.

There is something special about the fasting

that occurs during sleep

because it’s associated with a number of processes

that relate to the so-called glymphatic system,

the movement of lymph-like fluids

and other fluids through the brain,

a kind of sweeping out garbage disposal, if you will,

a clearing out of the metabolic debris

and some of the autophagy that’s associated

with bad processes in the brain.

So we could do a whole episode on this,

but essentially during sleep

and in particular during fasted states of sleep,

we are undergoing a number of automatic cellular processes

that clear out debris from our brain,

enhance cognition or at least offset dementia.

This is now well-established,

as well as a number of the same processes

occurring in the organs of our body.

So what we’re starting to see here

is that there are a number of constraints

on when you can eat.

Now, I would be remiss if I didn’t acknowledge

the social constraints and the real life constraints.

Some of us, because we want to eat with our family

and because our family or our significant others eat

around eight or 9 p.m.

and that’s the only time we’re together,

you have to eat late in the day.

And that’s certainly not a sin.

I’m not saying that’s good or bad.

Here, we’re trying to establish, if you recall,

best, better, and worst.

So from both a practical and a health perspective

and a purely objective view

of how intermittent fasting works and can benefit us,

starting to eat each day somewhere around 10 a.m.

or around noon,

and then allowing a feeding window

that goes until six or maybe 8 p.m.,

that seems to me, at least based on the data

and what I understand about typical cultures

where people eat in the daytime and in the evening,

that seems to me like the kind of schedule

that will allow you to get the most

out of intermittent fasting, time-restricted feeding,

but does not set you up to be really out of sync

with the social rhythms in most cultures.

If you think about it from the perspective

of, say, a noon to eight feeding window,

what you’ll find is that you’re able to eat lunch

with others, if you like, or by yourself.

You will be able to eat dinner at a reasonable hour,

at least in most countries, in most cultures,

eating dinner somewhere between 6.30 and 7 p.m.

is typical.

When you say a feeding window that goes until eight,

that doesn’t mean sitting down to dinner at eight.

That means your last bite of food

or ingestion of any liquid calories was at 8 p.m.

Assuming that you go to bed somewhere between 10 p.m.

and 1 a.m., that allows this tapering off

or this transition from feeding to a fasted state

and still allows you to capitalize

on the special period of fasting

that is sleep-related fasting.

And again, I want to emphasize that the fasting

that occurs during sleep is vital

and eating too close to sleep will disrupt

that fasting-related sleep.

Now, there are a number of caveats

and details related to this,

and there’s an important caveat in detail

related to people that are specifically interested

in increasing or maintaining muscle mass.

So first, let’s talk about food volume and food type

and how that relates to whether or not you quickly

or slowly enter a fasted state.

Because clearly when we talk about a feeding window,

that feeding window could include

any number of different foods.

It could involve cake and ice cream, pizza, hamburgers,

plants, fruit, whatever it is,

or it could involve just fats or just proteins, et cetera.

There are at least three factors that are going to govern

how quickly you transition from ingesting food

to a fasted state.

Remember, as you ingest your last bite or sip of calories,

that’s not when the fast begins.

That might be when the fasting begins on your watch

or on one of these apps that I’ll refer to later,

which can help you track your fasting and eating windows,

but that’s not when it actually begins

because your body is still seeing food.

You’re actually carrying around food inside of you,

even though you’re not putting it into your mouth,

you’re still eating in some sense.

So it should be somewhat obvious that very large meals

are going to take longer to digest than very small meals.

So that will impact how slowly or quickly you migrate

from a fed state to a fasted state.

There’s no way I can spell out what exact volume of food

you should ingest based on the size of your stomach

and et cetera, but you’re all familiar

with being extremely full, very full, comfortably full,

somewhat full, or not feeling full and feeling hungry.

So learning to gauge food volume is important.

Also foods that include some fats or a lot of fats

will tend to slow gastric emptying time.

And depending on the kind of fats,

it could mean that a given meal is digested

within three hours versus five hours.

So more fats might be a large meal with a lot of fats

has been can take five or six hours.

A smaller meal with less fat

is going to be digested more quickly.

Consuming calories in liquid form is going to mean

that gastric emptying time is going to be faster.

And then of course there’s the glucose

and the insulin aspect to it,

which is that foods that lead to big steep rises in glucose

like pure sugars, then your glucose will drop.

However, if they’re combined with fats,

then it tends to be a more gradual rise in glucose

and it’s more sustained, et cetera.

Fibrous foods will also create a more long-lasting

sustained release in glucose.

The important thing here is to establish a feeding window

that you can comfortably manage, okay?

Meaning that on average,

you can obey a six hour feeding window

or an eight hour feeding window or a 10 hour feeding window.

And then to place that feeding window

in a social and life context

that you can manage on a regular basis.

Now there are two key points

that have been gleaned from the scientific data

about this feeding window and when to place it.

And this is based on a really important experiment

that Sachin and his colleagues have been doing.

There’s a website that they have,

zero cost website called My Circadian Clock.

You can go to this website free of cost.

There are a number of important resources there,

but what they’ve done is they’ve examined

the feeding behavior of thousands of people.

People will take a picture of the food they’re about to eat

and it enters into their account,

maybe your account if you create one on My Circadian Clock.

And they do this over many days or weeks.

What’s great about this is it establishes

what’s essentially called a fetogram,

a time in which people ate.

And a number of important findings have emerged

from these fetograms across large populations

of people in different time zones

with different schedules, et cetera.

First of all, almost everybody

underestimates their feeding window.

Meaning people who think that they are

on an eight hour feeding window or six hour feeding window,

when their data are analyzed,

it almost is always the case

that they’re actually on a feeding window

that’s one or even two hours longer than they think.

You think, well, how could that possibly be?

If people are taking their first bite at noon

and they’re taking their last bite at 8 p.m.,

well, that must mean that they are on that feeding window

of eight hours.

And it turns out that people cheat,

but they don’t cheat in any kind of obvious way.

They might have, you know, a glass of wine after dinner,

or they’ll have a cup of tea and a little bite of a cookie.

And so when people are honest and they are honest

in most cases for this experiment,

what you find is that most people’s eating window

is actually quite a bit longer.

So in discussing this with Sachin

and reviewing the literature,

it’s clear that if you’d like to be

on a 10 hour feeding window,

that you should probably select an eight hour feeding window

because there’s always a little bit of a taper

on either side of that eating window.

Very few people are extremely strict

about these eating windows.

It’s just hard to do in the context of life events

and social gatherings and family and so forth.

Okay, so as we build forward your ideal fasting

slash time-restricted feeding schedule,

we now have several different rules that we can list out.

First, at least no food for the first hour

after waking up, at least one hour.

Two, no food intake for two and ideally three hours

prior to your bedtime.

Three, if you want to select an eight hour feeding window,

then you should probably focus on a six

or seven hour feeding window because in reality,

your feeding window is going to be longer.

Reality meaning real life constraints.

And if you’d like to be on a 10 hour feeding window,

you should probably select an eight

or a nine hour feeding window

because the way it plays out is that people

almost always eat outside of their eating window somewhat.

The other nice thing about selecting

a slightly shorter eating window

than is comfortable for you is that it takes into account

that as you take your last bite

or your last sip of calories,

there’s this time or taper before which you are actually

in a fasted state.

And because you’re eating different things

on different days, presumably,

some foods leave your gut more quickly.

Some things spike your insulin

and your glucose more than others.

Sometimes you eat more fat, sometimes less fat.

This allows you to fall well within the margins

of the benefits of time restricted feeding

that have been demonstrated in humans,

which generally involve an eight hour window or so.

So I think this eight hour window or six hour window

is a good thing to shoot for, for most people.

Some people, and we will discuss the exceptions,

but some people truly are exceptions to this.

They just require more food.

And along those lines,

I just now briefly want to touch on some of the studies

that have looked at using a very short feeding window

of about four hours.

Nowadays, a number of people

are doing the so-called one meal per day

or are restricting their feeding window

to just four hours or six hours.

And that turns out to be an interesting strategy.

And the data around it actually are a little bit surprising.

One surprising thing to leap out

of this massive literature review

on time restricted feeding in humans

is that relatively short feeding windows

of say four to six hours

do produce a number of positive health effects,

things like increased insulin sensitivity,

which we know is good.

Remember type two diabetes

is a reduction in insulin sensitivity,

improvements in beta cell function in the pancreas,

decreased blood pressure, decreased oxidative stress,

decreases in things like evening appetite.

So positive health effects

and psychological effects in general.

However, they either produce no change in body weight

or they tend to produce even increases in body weight.

Now, of course, there’s variation between individuals

and between studies, but this is somewhat surprising.

So the eight hour feeding window

seems to be very beneficial

across almost all the parameters that we’ve discussed,

inflammation, weight loss, fat loss, et cetera.

And adherence, I should mention,

people’s ability to stick to the diet

seems quite good on this eight hour feeding windows.

But when people try and undergo

very short feeding windows of four to six hours,

it seems that they are overeating in that four to six hours,

at least overeating with respect to their metabolic needs.

Now, the contrast to this

is the so-called one meal per day schedule.

Very few studies on one meal per day.

One meal per day,

unless it’s a very, very long meal and sort of feast,

typically would not last four to six hours.

I guess it sort of depends on how you define a meal.

But when you look at the very few,

I should emphasize again,

very few studies on one meal per day,

people typically maintain or lose weight

on the one meal per day schedule.

So what we can say is that the seven

to nine hour feeding window

produces all of the major health benefits

of time-restricted feeding,

as well as being pretty straightforward

for most people to adhere to on a regular basis.

And on a regular basis turns out to be very important.

I’ll get back to that point in a moment.

Whereas the four to six hour eating window

doesn’t seem to serve people

as well as say a seven or eight hour eating window,

simply because people are overeating

during that eating window.

And the one meal per day,

while perhaps ideal for certain people’s schedules,

may actually cause people to under eat.

And in some cases that might be what people want.

They actually want to under eat.

But when we start thinking about performance

in work and in sport,

and when we start considering hormone health

and hormone production, fertility,

that’s when we can really start to look

at the seven to nine hour feeding window

versus the four to six hour feeding window

versus the one meal per day type feeding window

with some different objectivity.

We can start to look at it through a different lens

because it turns out that when you place the feeding window

and how long that feeding window is

actually will impact a number of other things

in particular hormones that can be very important

for a number of things related to sex and reproduction,

can be related to performance at work,

performance in athleticism.

And there are excellent studies on this.

So let’s explore those now.

So let’s talk about some conditions

where having the feeding window early in the day

would actually be very beneficial.

There was a study that was published recently

in Cell Reports, again, Cell Press Journal,

excellent journal, peer reviewed,

very stringent from Aoyama et al.

So this is A-O-Y-A-M-A et al.

This was published just recently in July, 2021

that looked at the distribution of protein intake

in different meals delivered either early in the day

or later in the day.

And I’m summarizing here quite a lot,

but I should mention that this study was performed

in both mice and humans, same paper, mice and humans.

And involved hypertrophy training,

essentially increasing the weight bearing of given limbs

to try and induce hypertrophy,

which is the growth of muscle tissue.

It does appear that muscle tissue is better able

to undergo hypertrophy by virtue of the fact

that there’s better or enhanced protein synthesis

early in the day because of the expression

of one of these particular clock genes called BMAL, B-M-A-L.

BMAL regulates a number of different protein synthesis

pathways within muscle cells,

such that eating protein early in the day

supports muscle tissue maintenance and or growth.

And in this study,

they also looked at the effects of supplementing

so-called BCAAs, branched chain amino acids,

which is popular in bodybuilding circles

and in strength training circles.

And BCAAs are essential components

of a number of different foods,

but can also be supplemented.

The takeaway of the study is pretty straightforward.

However, the takeaway is if your main interest

is maintaining and or building muscle,

then it can be beneficial to ingest protein

early in the day.

You would still want to obey this,

what we’re calling a kind of foundational rule

of not eating any food for the first hour post waking,

or at least the first hour post waking.

And the cutoff for when you would want to eat protein

would be sometime before 10 a.m.

And there I’m averaging across a number

of different situations.

But in general, this BMAL expression is such that,

let’s say you wake up at 7 a.m.

Your main interest is in hypertrophy

or maintenance of muscle.

Then you would want to ingest some protein

sometime before 10 a.m.

But obviously, if you’re interested in getting

the health effects of intermittent fasting,

that you wouldn’t ingest any food

for at least the first 60 minutes upon waking.

Now it’s not as if at 10 a.m. a gate slammed shut

and you can’t generate hypertrophy.

Of course, that’s not the case.

However, it’s very interesting that it doesn’t matter

when the resistance training,

the load bearing exercise occurs in the 24 hour cycle.

So whether or not, in other words,

people are training early in the day

or they’re training late in the day,

it still appears that ingesting protein

early in the day favors hypertrophy.

Or that one is better, or I should say more easily

able to access hypertrophy by way of these clock regulated

protein synthesis mechanisms by ingesting protein

early in the day.

In no way, shape or form does this study say

that ingesting protein later in the day

is somehow bad for you.

It just emphasizes the positive effects

of ingesting protein early in the day

for sake of muscle maintenance and or hypertrophy.

So if you’re somebody who’s mainly concerned

with muscle maintenance and hypertrophy,

then it may make sense to move that feeding window

earlier in the day.

And certainly there are people out there

who are interested in muscle maintenance and hypertrophy

who aren’t doing intermittent fasting at all.

And that’s also perfectly fine,

but this just so happens to be an episode

about intermittent fasting and time restricted feeding.

There are of course, modes of eating where one eats

small meals spread throughout the day

or weights meals differently such that meals early

in the day are larger than later in the day or vice versa.

There are in a near infinite number of ways

to organize this.

But if you are somebody who’s interested in deriving

the many clearly established health effects

of time restricted feeding,

and you are somebody who would like to maintain

or build muscle,

then ingesting proteins in the early part of the day

would be important to you,

at least on the basis of these results.

And therefore that eight hour window

that we’ve established as more or less ideal

shifted to the later part of the day

might not be as beneficial for you.

Now I can just personally say that for me,

when I wake up in the morning,

it’s very easy for me to not eat until noon

or one or 2 p.m.

Eating early in the day is actually somewhat of a challenge.

I discussed this point with Sachin

because we were talking about how is it that one

can move their feeding window

or place themselves onto a different schedule

of intermittent fasting.

And it’s very clear that one needs to provide

a transition period in order for that to happen.

You should allow yourself a transition period

of anywhere from one week to 10 days

in which you shift your feeding window

by about an hour each day or so.

And then once you establish a feeding window

that feels comfortable for you

and that you think you can maintain over time,

that you simply maintain that feeding schedule

for at least 30 days,

but ideally you would do that indefinitely.

Now, this turns out to be important based on data

that they’ve gleaned from this my circadian clock,

massive experiment that they’ve been doing

where people are entering the times

that they’re feeding and eating.

Excuse me, anytime we talk about mice,

I always think about feeding

because I come from a background

and my lab works on both laboratory mice and on humans.

Anytime I think about humans, I think about eating,

but of course they are the same thing.

The interesting thing to emerge

from that very large data set in humans

is that when people log their feeding times,

as I mentioned before, oftentimes they think

they’re eating in an eight hour window,

but they are actually eating in a much broader window.

However, even for people that are very good

about restricting their feeding to a four or six

or eight hour window, if they’re very strict

about the start and stop times of when they ingest calories,

one of the findings that’s really been important to note

is that almost every individual has a lot of drift

in when that eating window resides in their 24 hour period.

In particular on the weekends,

people are either extending or shifting their feeding window

in a way that makes it seem that they’ve traveled

to another time zone and are eating

according to another time zone.

And this is extremely important.

As I mentioned earlier, based on the 2012 study

from Sachin’s lab, we’re eating at a particular phase

of each 24 hour cycle can help enhance the expression

of these clock genes.

If you are eating within a very strict

or semi-strict feeding window,

but that feeding window is migrating around from day to day

or five days a week, you’re really organized

about when that falls, let’s say for sake of example,

from noon to 8 p.m., noon to 8 p.m., Monday,

noon to 8 p.m., Tuesday, Wednesday, noon to 8 p.m.,

Thursday, and so forth.

But then on a Saturday, it’s becoming 11 a.m.

and you’re ending it early,

or perhaps you’re starting early in the day on Sunday,

you’re having brunch that starts at 9.30 or 10,

and then it’s extending out still just eight hours,

but it’s shifting around.

That can cause disruptions

in these circadian clock mechanisms

that cause disruptions in the downstream effects of eating

that are taking at least two to three days to recover from.

So obviously we don’t want to be overly neurotic

about this stuff, but because this is an episode

about the science of intermittent fasting

and time-restricted feeding,

as important as how long your feeding window is,

is where that feeding window resides in each 24 hour cycle.

And perhaps even more important than that

is that it be fairly regular

where that feeding window resides.

Because even if you have a very short feeding window,

if it’s drifting around from day to day,

that actually offsets a number of the positive health

effects of intermittent fasting.

So to really just underscore the way

that these different pieces

of the biological puzzle fit together,

if you are very strict or semi-strict

about your eight hour feeding window,

but on the weekends that eight hour feeding window

is falling later than it normally would

during the middle of the week,

it is as if you are going to bed later,

even if you’re going to bed at the same time,

at least from the perspective of metabolic health,

because of the way that eating impacts these clock genes

and impacts, or I should say,

subtracts the sleep-related fasting

that you would normally experience

if you were to finish eating a couple hours before bedtime.

So again, we don’t want to create any overly obsessive

or neurotic focus on this.

I think that most all people could benefit

from a time-restricted feeding schedule,

but they should really think hard about

what they can stick to on a regular basis

and understand that they tend to underestimate

the feeding window that they actually are partaking in

and that they should place that feeding window

in a portion of the 24 hour cycle

that they can be consistent on most days.

And I want to emphasize most again,

because we are not laboratory mice.

We don’t have a graduate student coming in

for eight hours a day,

because that’s what their significant other

will allow them to do.

And then removing the food from our jowls

and from our cages,

we have access to food pretty much 24 hours a day.

Along those lines, however,

there are things that we can all do

that will allow us to offset some of the drift,

if you will, that we experience,

or that we induce in terms of

when our feeding window occurs,

or that the feeding window might push out a little later

and then therefore start a little later the next day.

There are things that we can do

and there are things that we can take.

And so I’d like to discuss those briefly.

So throughout this episode,

I’ve more or less been alluding to the fact

that when you eat,

there’s some period of time afterwards

in which you’re actually still eating,

at least from the perspective of metabolism,

because glucose is up, insulin is up,

and you’re undergoing different metabolic

and digestive processes that don’t really speak to you

being in a fasted state, right?

It’s not just about when you take your last bite

or your last sip.

However, there are things that we can do

to accelerate the transition from a fed state

to a fasted state.

And so I’d like to discuss what those are.

And I want to emphasize that the term fed state

is probably a better way to think about it

than eating or not eating,

because we think of eating as the verb,

we’re eating, we’re eating,

okay, we’re done eating, I’m fasting now,

but you’re not actually fasting because you are fed.

So we should really think about fed and unfed states,

because from a cellular processes perspective

and from a health perspective,

that’s actually what your body and your system

are paying attention to.

And by now with everything that we’ve laid out,

I think that should be intuitive to understand.

So there’s a fun and exciting concept related to this,

which is glucose clearing.

You may have heard the old adage

that if you take a 20 or 30 minute walk after dinner,

that it accelerates the rate at which you digest that food.

And indeed it does.

Clearing out of glucose from your system

can be accomplished through a number of different means,

but light movement or exercise

does increase gastric emptying time.

So for instance,

if you were to eat a meal that ended at 8 p.m.

and then plop to the couch,

watch TV or get on your computer or go to sleep,

it would be five or six hours

until you have transitioned from a fed state

to a fasted state.

However, you can accelerate that considerably

by taking a 20 or 30 minute, just light walk.

It doesn’t have to be speed walking.

It certainly doesn’t have to be jogging,

but just walking outside or moving around.

So glucose clearing is an important aspect

of the transition from the fed state to the fasted state.

And just a light walk can allow you to do that.

Now, if you can’t get outside,

some people will go through the gymnastics,

literally of doing things like air squats and pushups

and things like that.

And indeed, those will increase the expression

of things like glut four

and things that mobilize glucose into muscles

and things of that sort.

But, you know, under most conditions,

most people aren’t doing pushups after dinner,

or certainly if you’ve had a big meal,

just taking a light walk can be beneficial.

In addition, you could consider doing intense exercise.

Now, you wouldn’t necessarily want to do that

immediately after eating.

So let’s take a look at what high intensity training

of any kind does to blood glucose.

Because in this case, it turns out

that when you do high intensity training,

actually has opposite effects on blood glucose,

depending on whether or not you do it early

or later in the day.

So a fairly recent study looked at so-called HIIT training,

high intensity interval training,

which of course can take many different forms.

It can take the form of circuit training with weights.

It can take the form of, you know, burpees and pushups

and sprints and all sorts of different things.

But high intensity interval training is typically training

that gets people’s heart rates up, you know,

well above 70% of maximum,

and then brief periods of rest and then repeating.

And how long the high intensity interval training,

of course, will also vary.

There are very brief, you know,

six or 12 or 15 minute workouts.

Some people can carry on with high intensity interval

training for up to 45 or maybe even 60 minutes

in extreme cases.

But when you look at the studies that have explored high

intensity interval training and its effect on blood glucose,

there are a couple of studies that leap out.

For instance,

one that emphasized that blood glucose levels will actually

increase if high intensity interval training is performed

early in the day and will decrease if high intensity

interval training is performed later in the day.

Now the purpose for this exploration was not to explore

clearance of blood glucose for sake of intermittent


It was mainly focused on athletic performance and whether or

not that was better early in the day or later in the day,

et cetera.

But we can extract some information from these studies that

are beneficial for sake of understanding glucose clearing.

If you have ingested food throughout the afternoon and

evening and late in the day,

and you’re thinking about going to sleep and you’d like to

enter sleep in a way that is less fed and more fasted,

then engaging in high intensity interval training in the

afternoon will lower or evening, I should say,

will lower blood glucose.

And in that way will help you accelerate your transition

into the fasted state,

provided you don’t ingest something after the high intensity

interval training.

Now is the increase in blood glucose that occurs from high

intensity interval training early in the day?

Is that detrimental?

Not necessarily.

So that oftentimes is associated with the shuttling of

nutrients to the muscles that have just done a lot of hard


So it’s not that high intensity interval training should not

be done early in the day.

In fact, for many people, including myself,

training early in the day,

just for the way that my psychology and biology works is

always better for me than training later in the day.

And the other important thing to mention is that high

intensity interval training done late in the day can be

beneficial from the perspective of glucose clearing,

lowering blood glucose and helping transition from the fed

to the fasted state in preparation for sleep.

However, if you’re ingesting caffeine or anything to engage

in that high intensity interval training in a way that

prevents you from getting to sleep,

well then it’s going to be detrimental overall.

So the reason I mentioned this is of course,

because it’s nice to know that light walks after dinner or

any other meal for that matter,

or high intensity interval training provided it’s done in

the second half of the day can lower blood glucose and

speed the transition from fed to fasted states.

But I also mention it because what we are really trying to

achieve when we partake in intermittent fasting,

so-called time restricted feeding is what we’re really

trying to do is access unfed states or fasted states.

It’s not really about when you eat and what you do.

It’s about extending the duration of the fasting period as

long as you can in a way that’s still compatible with your

eating, right?

Not the other way around.

And this gets back to this key feature of our biology,

which is that what we eat, when we eat,

when we exercise, when we view light,

it’s about setting a context or a set of conditions in your

brain and body.

So it’s not so much about the activities that you undergo.

It’s about the activities you undergo and their relationship

to one another over time.

And so in this way,

it really beautifully highlights the way that your biology is

interacting all the time.

Light is setting when you’re going to be awake and when

you’re going to be asleep.

When you eat is going to be determining when you’re going to

be awake and when you’re going to be asleep.

And when you eat is also going to be determining when you are

able to clear out debris from your brain and body and repair

the various cells and mechanisms of your body.

When you’re able to reduce those inflammatory cytokines

throughout your body.

And this is really the beauty of time-restricted feeding,

which is it’s not really about restricting your feeding.

It’s about accessing the beauty of the fasted state.

Now there are other ways to clear out blood glucose that

involve supplements or prescription drugs.

These are so-called glucose disposal agents,

glucose disposal agents, such as metformin,

which is a prescription drug or berberine,

which is an over-the-counter substance will lead to very

traumatic reductions in blood glucose.

And so they shift you from a fed to a fasted state.

And I know many people who take berberine before eating

meals that include a large number of carbohydrates,

for instance, as a way to clear out glucose.

Now I’ve tried berberine before.

And what I can tell you is that if you take berberine,

which by the way is very much like metformin,

its effects are almost identical to metformin in fact,

but it’s much less expensive and it’s over the counter.

If you take berberine and you have not ingested

carbohydrates, many people, including myself,

experience a splitting headache.

You become hypoglycemic because it is a glucose clearing


So if you’re going to experiment with things like metformin

and or berberine or similar,

you want to be very cautious that you’re not clearing out

blood glucose that’s already low.

And the dose response for this varies tremendously from one

individual to the next.

And there’s a strong circadian component.

So some people react very well to berberine early in the day,

but find that later in the day,

it provides extreme headaches for some people it’s the


So I caution you in exploring things like berberine and

metformin that you should expect to experience a number of

physical and psychological effects that may work for you

might be great for you, but might also not be great for you.

Nowadays, there are a number of commercially available

continuous glucose monitors.

I’ve tried one of these.

It involves putting what’s essentially a patch with a little

needle that goes into your skin, which is continuing,

continually, excuse me,

monitoring your blood glucose and you can look at it at an

app on your phone.

And you can learn a lot that way about how different foods

impact the increases and decrease in blood glucose.

If you’re doing experiments with berberine or metformin,

you can see how those impact your blood glucose.

You can see how exercise hit training or otherwise in black

impacts blood glucose, excuse me again,

it’s very hard to assess blood glucose without a continuous

blood glucose monitor.

And if you’re not using one,

you’re mainly going to be relying on subjective things like,

oh, I feel like I have low blood sugar, or I feel shaky.

Like I have high blood sugar or shaky.

Cause you have low blood sugar.

So I have to say that glucose clearing agents that involve a

walk or exercise moderate or intense are going to be a lot

easier to titrate and adjust the levels of than things that

you’re going to take, where you have to ingest the dosage.

And then once you ingest a certain dosage,

you’re along for the ride,

at least until the effects of that particular compound

wear off.

It doesn’t mean those things don’t have utility.

It doesn’t mean people aren’t using them because many people

are, but they are potentially a very sharp blade.

That is a double sided blade.

So I encourage you to approach those with caution.

If you decide to at all,

it’s worth thinking about what the low blood glucose state

is and why it’s beneficial as well as why it might produce


And in some cases can also adjust the effects of other

hormones in the fasted state,

a number of different proteins that are expressed in cells

undergo changes in their expression.

We talked about this earlier.

When we are fasted,

we tend to reduce the activity of a particular protein

called mTOR, mammalian target of rapamycin.

mTOR is very active in cells while they are growing.

So throughout development,

it’s also very active in cancers of various kinds.

mTOR needs to be what’s called phosphorylated.

If you don’t know what that means,

don’t worry about it.

But phosphorylation is a manner in which certain proteins

are altered so that they can actually be functional within


mTOR is associated with cell growth of all kinds,

healthy and unhealthy.

When mTOR is phosphorylated,

there’s a marker called PS6.

So phospho mTOR expresses PS6.

If this is all escaping,

you don’t worry about it.

Phospho mTOR and PS6 are reduced by fasting.

Now this makes sense if you think about it because eating

and growth are associated with each other.

Fasting is not necessarily anti-growth,

but it is not pro-growth.

And when we fast,

we see increases in cells of things like AMPK,

the sirtuins,

things like transcription factors,

like FOXO, ATF and ketones or ketone bodies.

You may have heard of the ketogenic diet.

What’s the point of all this biochemistry?

It’s not just blitz you with a bunch of cellular biology and


It’s to say that we have cell growth pathways involving mTOR

and PS6,

and we have cell repair and cell shrinkage processes that

are associated with AMPK,

the so-called sirtuins,

which Dr. David Sinclair from Harvard and others are famous

for discovering and understanding things like AMPK.

These two different divergent pathways of cell growth and

cell breakdown and repair.

And by breakdown,

I mean actual clearance autophagy and repair.

Those can be triggered by being in either the fed or the

fasted state.

So one way I’d like you to think about the fed state,

not just eating,

but having recently eaten or the fasted state,

meaning high blood glucose and,

or you’ve recently eaten or are currently eating or drinking

calories is that when you eat or when you don’t eat,

when you’re fed,

when you’re fasted,

you are either promoting cellular growth of all kinds,

or you’re promoting cellular repair and clearance of all


And so again,

this is about setting conditions in the brain and body.

It’s not so much about when you eat food A or B,

it leads to increases in mTOR.

Anytime you eat any food,

doesn’t matter if it’s plant-based, animal-based, fat,

protein, carbohydrate, doesn’t matter.

You are biasing your system towards a biochemical state of

cell growth.

And anytime you haven’t eaten for a while or blood glucose

is low,

you’re biasing your system toward a state of cellular repair.

And this is why people who do not suffer from any blood

glucose regulation issues,

take things like Berberine as glucose disposal agents or

take Metformin.

I’m not necessarily suggesting that you do that,

but it’s because those things mimic fasting.

They create situations in the body that promote things like

AMPK and the sirtuins and others to push your body and your

system down a route of repair,

even though you might’ve just eaten a meal an hour ago.

Along the lines of the health benefits of intermittent


there are nice data showing improvements in the gut


And in particular,

in the treatment of irritable bowel syndrome and other forms

of colitis in time-restricted feeding,

meaning time-restricted feeding seems to be able to assist

people with those conditions,

following the general parameters that I discussed before

eight hours and so forth.

Why and how well by way of intermittent fasting impact in

the expression of these various clock genes.

And because the clock genes impact the mucosal lining,

the mucus lining of the gut,

it appears that intermittent fasting can reduce the amount of

so-called lactobacillus that’s present in the gut.

And lactobacillus is when in high levels is correlated with

a number of different metabolic disorders.

At the same time,

time-restricted feeding seems to enhance the proliferation of

some of the gut microbiota like a syllobacter and some of

the other ones that promote healthy mucosal lining and that

promote better overall intestinal function.

So these are pathways that have now been established and it

appears that intermittent fasting,

isn’t just modulating these processes,

but is actually having a direct effect on the mucosal

lining in a way that favors a healthier gut microbiome.

So it should come as no surprise that many people who

experienced gut issues benefit from restricting their

feeding window to eight hours or so per every 24 hour


The other very exciting finding about intermittent fasting

is one of the major health issues these days is the

proliferation of so-called non-alcoholic fatty liver disease.

30 years or so non-alcoholic fatty liver disease was

exceedingly rare to see in the clinic, except in alcoholics.

Fatty deposits in the liver are bad.

It is essentially liver disease.

Nowadays, children and adults are showing up with

non-alcoholic fatty liver disease.

Some of these people are obese, others are not,

but it’s a serious health concern.

And it’s growing in numbers all the time.

A recent study that was published in cell reports medicine

just a couple of weeks ago tested the hypothesis,

whether or not the gut microbiome or so-called brown fat

tissue is impacting the liver health.

And in particular, non-alcoholic fatty liver disease.

The short takeaway from the study is that contrary to what

was previously thought the gut microbiome,

while very important for a number of other processes in the

body doesn’t seem to be related to this non-alcoholic fatty

liver disease.

This is surprising to people or should be to those of you

that have been following the gut microbiome literature.

However, brown fat,

which is a healthy fat that we have between our two

scapulae and in our upper neck,

it doesn’t tend to be blubbery type fat pads,

but it sits deep to the skin,

but creates a thermogenic effect in the body that is helpful

for reducing the amount of other fat,

the type of fat that we’re more typically used to thinking

about and talking about white fat and pink fat.

That’s subcutaneous fat around the abdomen and so forth.

Brown fat seems to have a direct correlation with the lack

of non-alcoholic fatty liver disease.

What this study showed was that in people that have

diminished concentrations of brown fat,

there is a higher probability of having non-alcoholic fatty

liver disease.

Now the good news is brown fat stores can be increased.

And again, this isn’t going to create blubber of brown fat.

This is going to create increased thermogenesis and actually

make people leaner.

And brown fat has a number of other important positive


Now this is interesting because cold exposure of anywhere

from one to three minutes,

two or four times per week, or maybe even 10 minutes,

two to four times per week can increase brown fat stores.

Also time-restricted feeding has now been tied to the

density of brown fat stores.

So time-restricted feeding also seems to positively

increase brown fat stores,

probably because of the way that brown fat stores relate to

epinephrine and adrenaline,

which tend to go up when we’re fasted.

What does this all mean?

This means for sake of liver health and for sake of reducing

or maybe preventing, or even potentially,

want to underline potentially reversing non-alcoholic fatty

liver disease,

time-restricted feeding also appears to be beneficial.

Many people out there are interested in optimizing their


And as we mentioned earlier,

insulin is a hormone and time-restricted feeding seems to

have very positive effects on overall insulin profiles and

so forth.

But anytime you mentioned hormones,

people immediately seem to leap to the sex steroid hormones,

testosterone and estrogen,

because indeed they have powerful effects,

both in the short-term and the long-term in terms of our

mental and physical health and performance.

There’s at least one study that’s explored the effects of

time-restricted eating on performance,

athletic performance, immune function, and body composition.

This was a study by Morrow et al that was performed on

elite cyclists.

So I want to point that out.

It was a randomized control trial,

but what’s really nice about this study is that it explored

a number of different hormonal parameters in people that

were using time-restricted eating or that had a more

extended eating window.

And they tracked everything very carefully.

And the amount of food they were eating was actually pretty

considerable, 4,800 calories.

So that’s a lot of calories, but then again,

they were very active and they measured a number of different

things related to VO2 max, et cetera,

performance and overall performance at what they did,

cycling is not the point that I want to emphasize here.

Although there were some positive effects on their

performance related to time-restricted eating.

The point I want to talk about relates to things that

presumably relate to most everybody,

which are the effects on things like glucose,

thyroid hormone, testosterone, sex hormone,

binding globulin,

which can bind up testosterone and prevent the so-called

free form of testosterone,

which is the one that has most of the actions in the brain

and body.

And the major takeaway from this study was that time

restricted feeding of the same amount of calories as the so

called control condition, okay.

Same calories,

but either compact throughout the 24 hour cycle to an eight

hour feeding window or allowing them to eat over a larger

feeding window did lead to significant decreases in free


And I think a number of people will raise their eyebrows to

that and think, oh,

well then maybe time-restricted feeding is not for me.

There are a number of important considerations.

Of course,

one is while the decrease in free testosterone was


it’s also going to depend on where people start out.

So if somebody has already low or modest levels of

testosterone and it drops by 10 or 20%,

that could lead them into a state of poor performance and


Whereas if somebody has higher testosterone,

a decrease won’t necessarily do that.

So it’s important to take that into consideration.

This is why I’m always such a fan of people doing their

blood work and knowing what’s going on under the hood for


A very interesting change in hormonal profile was cortisol,

so-called stress hormone.

Cortisol of course is also naturally released early in the

day in a healthy way to wake you up and promote alertness,

but you don’t want its levels to be too high or to have

peaks in cortisol late in the day.

It’s actually correlated with depression and a number of

other untoward things.

I would have thought that by restricting a feeding window to

a particular time each day that these hard training

cyclists would have undergone increases in serum cortisol.

And in fact, the opposite was true.

They had significant reductions in serum cortisol as a

consequence of time restricted feeding.

I should mention there were significant reductions in serum

cortisol also in the control group,

but not to the same extent.

And the two groups did differ significantly from one


Now this is important because if you just look at one

hormone testosterone, you’d say, okay,

based on these data,

time restricted feeding is reducing testosterone levels


even though the number of calories is quite high and is held

constant across the study.

But in fact, because cortisol is lower,

it may mean that the effects of testosterone or the

reduction in testosterone is offset.

And that’s because cortisol and testosterone are always in

this somewhat of a dance in terms of cortisol,

inhibiting the effects of testosterone largely and vice


So it is interesting and important to look at the total

gallery of hormones.

And they did look at a number of hormones.

They looked at other inflammatory markers.

Those were not increased.

That’s not surprising.

If you remember back to the 2012 Sachin Panda study,

this early pioneering study on time,

restricted feeding,

they saw reductions in stress hormones and in inflammatory

markers in time, restricted feeding mice.

And here, this also seems to be the case in humans.

So the takeaway is for sake of hormone health,

time restricted feeding is compatible with quality hormone

health, even in high-performing athletes,

based on everything we know and that we’ve discussed,

I would not suggest that people restrict their feeding

window to less than eight hours,

especially if they’re training hard on a regular basis.

And it’s not just athletes that should pay attention to


When we are working very hard,

when we are psychologically stressed,

when we are studying for exams or we are in conflict with

somebody on a regular basis,

that creates a stress in the body.

That’s very similar to that of physical training,

the body and brain don’t distinguish between physical stress

and mental stress.

It’s all nervous system.

Remember that it’s just cortisol and adrenaline.

There’s no special hormone just for physical stress versus

psychological stress.

So again,

in thinking about what sort of feeding window will be right

for you,

I would look back at this eight hour time bin that seems

more or less flexible for most conditions,

even high-performing elite athletes.

And I would say just by logical extension,

even for people that have a lot of stress in their life.

And I personally wouldn’t suggest that people who have a lot

of stress in their life or the potential for stress in their

life, shorten their feeding window,

much shorter than eight hours,

because then you would expect that you would start to

increase some of the inflammatory markers.

You would increase the stress hormones and you would be

decreasing things like testosterone and estrogen,

some of the sex steroid hormones.

So again, it’s all about context and the eight hour window,

it isn’t holy,

but seems to be a really useful guide to extract the great

health benefits of which there are many in of which we’ve

discussed from intermittent fasting,

time-restricted feeding,

and yet that it could still be compatible with decent social

schedules and for maintaining hormone health.

In keeping with this for women that are trying to maintain

ovulatory cycles or for couples that are trying to get


I think it’s also important to not create a feeding window

that’s too short.

The relationship between feeding and body fat stores and

glucose and leptin and hormones is a well-established one.

And we can summarize it very easily here.

Although I’ve done several episodes related to this

previously on optimizing hormone health,

but basically we undergo puberty when there’s enough food

and there’s enough body fat that the body fat sends a signal

to the brain called leptin.

And that’s a hormone that comes from body fat signals to the

brain to turn on puberty that’s puberty.

But even as adults for women that are menstruating,

there needs to be sufficient leptin signaling to the brain in

order to maintain ovulation because of the way that the brain

communicates with the pituitary and the ovaries.

Similarly for men fasting or extreme exercise plus fasting,

we now know reduces testosterone.

Its impacts are not exactly clear.

However, if you reduce food intake,

either in total calories or in duration too much,

you will suffer a drop in sperm counts.

Fertility will drop.

And this makes sense.

The body is communicating to the brain,

whether or not conditions are sufficient in the body to

reproduce and to presumably,

and hopefully support the health and wellbeing of those


So there’s a logical link between body fat and eating and

how much food is available to you and how long it’s

available to you and the signals in the brain that allow for

reproductive success.

There are some data that point to differences in the effects

of intermittent fasting for males versus females.

Those data right now only come from mice.

That study was published by Sachin Panda recently.

We still await the studies in humans.

Some people do not do well on intermittent fasting,

either in terms of mood or hormone health.

And so everyone needs to determine for themselves,

whether or not having a time-restricted feeding window is

good for them.

How long that time-restricted feeding window should be.

I think eight hours is kind of a nice minimum to adhere to

based on everything that we’ve covered today.

And for some people time-restricted feeding is not going to

be compatible with hormone health for them,

eating more meals spread throughout the day,

presumably smaller meals,

same caloric intake is going to be more beneficial for

their hormones.

This is something that is going to be individual and is

going to have to be determined on an individual basis.

However, if you’re going to try time-restricted feeding,

I do want to remind you that taking a period of three to

seven or ideally 10 days to transition into it,

not just going flipping from eating to three meals a day

that span from 6am to 10pm and suddenly going to an eight

hour feeding window,

but rather winnowing down that feeding window about an hour

or so per day is going to allow the hormone systems of your

body, including leptin, the hypocretin erection system,

which are systems within the body that signal to the brain

that food is about to come,

allowing those systems to adjust so that you’re not

overwhelmingly hungry, irritable,

and you’re not throwing your whole hormone system out of


I keep coming back to this eight hour feeding window and I

want to provide a little more basis for it.

And just to encourage that it’s not completely arbitrary,

the lengthy review that I mentioned earlier features a

number of studies that have used this eight hour feeding


but there’s a particular study that I’d like to highlight

mainly because I don’t expect people to delve into the full

reference list of the other review.

And this is a study that was carried out between such in

Panda’s lab and Christopherities labs.

This is a collaboration.

The study was carried out in humans and is entitled effects

of eight hour time,

restricted feeding on body weight and metabolic disease,

risk factors in obese adults, excuse me.

And this study essentially showed,

I’ll just read the conclusions that an eight hour time

restricted feeding produces a mild caloric restriction and

weight loss without calorie counting.

So that’s key, right?

These people aren’t calorie counting somehow just by

adhering to an eight hour window,

they are taking in fewer calories than they’re burning off

and clinically it reduced blood pressure.

So I mentioned the study,

not because there aren’t many others involving the eight

hour feeding window also in humans,

but because the eight hour feeding window has been tested in

obese adults and non-obese adults.

And there are even a few studies in children.

So this eight hour window seems to be a really good rule of

thumb and a kind of anchor around which we can each think

about incorporating time restricted feeding.

There are of course other patterns of feeding.

And while some people have engaged in longer fasts of 24

hours, 36 hours or more alternate day fasting,

meaning eating one day, not eating the next day,

or in some cases eating one day and eating very few

calories, 500 or 600 calories.

The next day has been tested.

A few studies have also looked at eating a sort of

maintenance level of calories for five days and then taking

two days and fasting clear through or eating very few

calories, you know, 300 or 500 calories.

In fact, there’s a sort of a community online of people that

are exploring longer fast for sake of trying to offset

dementia or reverse effects of dementia.

Thus far, at least in my awareness,

there isn’t any quality clinical peer reviewed study on that

yet for sake of dementia.

Although I await those studies.

And if anyone’s aware of them,

please send me a link in the comments,

but alternate day fasting has gotten the so-called safe bill

of health.

This has been written up,

meaning that people didn’t suffer bone loss.

They didn’t suffer any major detrimental effects.

It does seem that it can create significant weight loss and

can help with obese individuals that it can reduce resting

blood glucose.

And every other day fasting in many cases can produce more

rapid effects on weight loss and reductions in blood glucose

than time restricted feeding.

However, every other day type fasting for most people is not

going to be feasible.

They’re just not going to be able to do that for a long

period of time.

And what hasn’t really been done is the follow-up to see

whether or not people who do every other day fasting or five

days of eating followed by two days of fasting,

whether or not that leads to a rebound in weight gain,

whether or not that leads to a rebound in blood glucose,

et cetera.

So for now the eight hour feeding window and time

restricted feeding seems to be the most tested supported in

animal studies and in human studies.

And the one around which I think most people should orient

if they’re considering getting into time restricted feeding.

It’s also sort of hard to imagine how one could include a

significant exercise schedule or work schedule on every other

day fasting.

Remember in any study,

people are often being compensated or at least are

incentivized in some way to adhere to the study.

This is one of the major issues that I have with any study

that says that three or four different diets are essentially

equal in terms of their ability to produce weight loss.

Adherence is very different in the outside world where you

don’t have a researcher monitoring you where you’re not

logging all your food.

Most people don’t do that consistently.

And we can take a little bit of a neuroscience perspective

on this to try and arrive at what the best kind of

organization of eating plan,

or if we wanted to call it a diet,

we could would be for you.

Many people find it easier to just not eat for certain

periods of each 24 hour cycle than to eat smaller portions.

Portion control is very hard for some people,

for other people it’s manageable, but people like me,

I don’t eat half the croissant.

I don’t think it’s a real thing.

It’s not, it’s not available to me.

I should say now, of course I could eat just half a

croissant, but I noticed that when I eat the croissant,

because they’re so delicious that it creates a rise in blood

glucose, a rise in the other hormones and chemicals that are

associated with ingesting delicious, highly palatable food.

And it’s actually a lot of work for me to just eat half the


There’s something that’s much more thoroughly satisfying

about eating the entire croissant.

And actually there’s something that’s somewhat satisfying

about not eating the croissant at all.

And just knowing that later I can eat the whole croissant.

Now that’s me.

Other people find that they don’t have any trouble with

portion control,

that for them just eating small bits of food throughout the

day is what sets them in the right psychological and

physical state for sake of work, et cetera.

And I mentioned work and mental focus because one of the

aspects of fasting that have drawn a lot of people to time

restricted feeding and fasting is the clarity of mind that

people get when, first of all,

they don’t have to think about when they’re going to eat

because they know when their eating window begins.

They also don’t have to think about regulating their

behavior because they already know when they’re going to eat

and when they’re not going to eat.

Whereas when you’re restricting portions,

you actually have to make decisions all the while, you know,

and I think I, like many people decide, well, you know,

is that exactly half or could I have like another rung on

the croissant, this kind of thing.

I don’t negotiate with food.

That’s why I like a time restricted feeding window.

I know I’m going to eat for, in my case,

I use a 10 hour feeding window or so,

and I’ll eat the whole croissant.

I just don’t have to think about it.

Now the food choices that you make inside of that feeding

window are of course also going to be very important.

Certain foods will increase blood glucose such that you’re

going to get hungrier and hungrier.

Others will maintain lower blood glucose and will allow you

to be more controlled in the foods that you pursue.

Those are all individual considerations that are deserving of

their own entire episode.

But I do want to point out that the advantage of time

restricted feeding is that it involves a lot of the

decision-making in the brain.

The so-called go, no-go circuitries of our basal ganglia.

If you want to know this areas that control them,

anytime we have to restrict a behavior,

that’s called a no-go.

Anytime we engage in a behavior, that’s a go.

No-go behaviors require a lot of what’s called top-down

control, and it’s very metabolically demanding.

And so time restricted feeding allows you to depart from the

whole no-go, go negotiation that you have to undergo when

you have to restrict portions.

And so I think this is a reason why many people have

gravitated towards time restricted feeding and why,

for people that don’t want to have to think about all that,

it’s just very straightforward.

One of the more hot button issues out there is whether or

not given equal amounts of caloric intake and equal amounts

of activity and equal amounts of nutrients, et cetera,

whether or not restricting food to a particular window

biases more weight loss toward fat loss versus loss of

other tissues.

Because of course, when we lose weight,

we can lose that from any number of different storage sites

within the body, muscle, water, glycogen, or fat.

Now this is such a hot button issue that I almost don’t want

to get into it, but I’m going to get into it anyway,

because there are data that are very interesting.

This is covered in the review that I mentioned earlier that

describes how if people follow a time restricted feeding

schedule for long periods of time, so 60 days or longer,

there are some metabolic changes in the way that people

metabolize energy that do seem to shift the system toward

more fat loss relative to burning of other tissues when in a

state of caloric restriction.

And I want to say when in a state of caloric restriction,

because there’s really no way to cheat the system.

There’s no way that you can ingest far more calories than

you burn or excrete.

When I say excrete, you know,

I certainly don’t suggest this, but there, you know,

bulimics and other people that have eating disorders will

use laxatives as a way to eliminate food quickly from their

system so it can’t be converted into fat or other forms of


That’s a very, in that case, it’s a pathological situation,

but in general calories in versus calories out,

as I mentioned earlier,

is this kind of foundational element,

but in states of caloric restriction,

meaning sub-maintenance intake,

time-restricted feeding does seem to bias more of the energy

burned to compensate for that deficit from fat.

And the way it accomplishes it is very interesting.

It turns out that it drives more fat loss by way of

increasing a hepatic lipase.

This is something called LIPC,

hepatic means of the liver and lipase,

which anytime you hear ASE is means it’s an enzyme.

So it seems to increase hepatic lipase.

So it increases the enzyme that metabolizes fat for

lipolysis and energy production and reduces something called


which is a lipid droplet associated and lipolysis

inhibitor. Now that’s a mouthful, no pun intended,

but what CIDEC really is this lipid droplet associated

molecule is it can inhibit lipolysis.

So extended periods of time-restricted feeding,

meaning eight hour feeding window or 10 hour feeding window

that’s obeyed for several months or more seems to allow the

system to shift toward burning more fat or rather using a

higher percentage of fat when in a caloric deficit.

Now I doubt that this is going to resolve the truly barbed

wire, almost hairball,

ridiculous online debates about whether or not time

restricted feeding is better than another feeding schedule.

Look, I don’t think any particular feeding schedule is holy.

If you are sub caloric,

meaning fewer calories burned than calories ingested,

you’re going to lose weight.

But the data seem to point to the fact that if you do time

restricted feeding for a fairly long duration of time,

and you maintain that,

that you are increasing these lipases that increase

lipolysis energy use from fat,

and you are decreasing the lipid droplet associated

lipolysis inhibitors.

So it’s both a,

you’re removing the brake and you’re pressing on the

accelerator of fat loss.

I think that this logically points to a case in which using

time-restricted feeding with a sub caloric intake seems to

be at least to my mind,

the most scientifically supported way to ensure that a

significant portion of the weight that one loses is from

body fat stores.

Any discussion about fasting would be incomplete without a

discussion about what does and does not break a fast.


there is no black and white answer to that question.

And you should immediately understand why it’s because

eating and not eating are not equivalent to fed and fasted.

It depends on when you ate,

how much you ate and where you are in your circadian cycle.

We can actually arrive at a simple answer to whether or not

something breaks the fast or not.


the technical way to go about this would be to wear a

continuous glucose monitor and to ingest little bits of food

of different kinds or large amounts of food of different

kinds and measure blood glucose,

because ultimately blood glucose is the readout of whether

or not your system is in a fed or fasted state.

There are other parameters too, of course,

but that’s the dominant one.

Insofar as the scientific literature says,

drinking water will not break your fast.

Drinking tea will not break your fast.

Drinking coffee provided it is black coffee will not break

your fast.

Ingesting caffeine in pill form will not break your fast.

There are other things that won’t break your fast.

For instance,

eating one peanut when deep in a fasted state will not break

your fast.

Eating a whole handful of peanuts might not even break your

fast if you are in a very low glucose state.


if you just finished a meal that included carbohydrates or

it was a very large meal of any kind an hour ago, yes,

indeed eating one peanut could break your fast.

So it’s all contextual.

That’s what’s really important to understand unless you’re

going to wear a continuous glucose monitor.

And unless you’re going to wear a continuous glucose

monitor and set an absolute numerical threshold for what it

is to break your fast.

I think there are some simple rules that we can follow.

First of all,

anything that involves sugar in particular,

simple sugars can potentially break your fast.

And there’s actually a study on this,

which shows that if people ingest even one,

one gram of sugar post dinner,

if they had a full meal for dinner,

that can actually disrupt the expression of some of the

circadian genes related to fasting and to sleep and sleep

related fasting.

Now that’s pretty extreme.

It’s almost kind of scary to think about,

but that’s how sensitive our system is.

If we already have somewhat elevated blood glucose from a

meal that we ate an hour or so ago,

whereas if we have run for an hour or trained hard,

high intensity training,

and we haven’t quite reached the beginning of our so-called

feeding window,

will eating a small amount of food take us out of that fast?

Well, depends on what the food is.

If it’s mostly fat, probably not.

A number of people out there nowadays talk about so-called

fat fasting.

Fat fasting is a way to kind of regal past the stringency of

either eating or not eating as a black and white rule for

feeding window versus non-feeding window.

So some people will ingest medium chain triglycerides,

so-called MCTs,

or people will ingest fats only until their official

feeding window begins.

So these are sort of how the negotiations that people carry

out tend to go.

But fat of course,

won’t increase blood glucose and insulin as much as

carbohydrates will.

Protein will have sort of an intermediate effect.

And as I mentioned earlier,

ingesting carbohydrates with some fat will tend to blunt the

rise in glucose and will extend the duration over which

glucose is released.

So we really can’t say food X or beverage X breaks a fast.

However, at the extremes, we can say that, for instance,

if you drink a can of soda pop,

unless you just ran an ultra marathon,

you’re breaking your fast.

Okay. Eat a piece of pizza.

You’re breaking your fast.

If you eat purely fats, maybe, probably not.

If you’ve been fasting for five hours or more,

strictly fasting for five hours or more.

So you can start to see where there’s a lot of wiggle room

and it’s very contextual.

And this is why any posts that you see,

or any information that you see that something does or does

not break your fast,

that doesn’t place it in the context of when the last time

you ate and what you ate and your activity and your time

within the circadian clock schedule of 24 hours.

It’s a sort of meaningless discussion.

So in general,

I think what’s really useful if you’re not going to wear a

continuous glucose monitor is to try and be fairly strict

about when you initiate your feeding window.

And when you stop your feeding window,

and as time evolves and you establish a more regular routine

of eating certain kinds of foods and not others that are

right for you.

Cause as I’ve emphasized before on this podcast,

and I will continue to emphasize,

keto works great for some people.

Vegetarian keto works great for some people.

Carnivore diet works great for other people.

Some people are omnivores.

Some people are carnivores.

Some people are vegan.

All of that is great and fine by me.

Everyone has to establish what’s right for them today.

We’ve really bypassed the discussion about foods of a

particular origin or type animal-based or plant-based,

but all the same rules apply within this thing that we’re

called intermittent fasting or time-restricted feeding.

So what breaks a fast will depend and what you want to eat

or what you are willing to eat.

That’s a totally separate manner from when you eat.

But as we’ve established, when you eat is vitally important.

Some of you are probably wondering whether or not artificial

sweeteners or non-artificial plant-based sweeteners like

Stevia break a fast.

This will vary somewhat.

And I have to say the data on this are somewhat mixed.

There is evidence that when people ingest artificial


that it can create a transient increase in blood glucose

followed by a transient decrease in blood glucose below


This is thought to explain the increase in hunger caused by

ingestion of things like aspartame and sucralose and things

of that sort.

There are not a lot of good studies exploring the plant

based non-sugar sweeteners, things like Stevia,

even things like monk fruit,

which is a separate category into itself.

There aren’t a lot of studies on this.

I think most people need to establish this for themselves.

The best way of course,

would be to wear a continuous glucose monitor to go into a

fasted state of either one hour or two hours,

or maybe you’ve been fasting all night and then ingest

Stevia in whatever form you want or coffee in whatever form

you want with sucralose or aspartame, et cetera,

setting aside the discussion about the effects of these

things on the gut microbiome,

which is a different topic entirely.

I think it’s fair to say that in moderation,

the plant-based non-sugar sweeteners like Stevia in

particular Stevia seem to have a minimal impact on overall

blood glucose when considered over a fairly large time bin

aspartame and sucralose, saccharin,

I think we can say more or less the same,

but as soon as you get into a discussion about those,

you also have to get into a discussion about some of the

evidence published in nature and other excellent journals

now pointing to the fact that when consumed in excess,

not when consumed in moderation,

but when consumed in excess that those might have some

detrimental effects on the gut microbiome.

So do artificial sweeteners break a fast depends on the

amount depends on the type. And in general,

I think you’re probably okay,

provided that you’re not indulging in them too often.

However, some people,

just by virtue of tasting something sweet,

feel a spike in their appetite that makes it harder for them

to adhere to the feeding window.

And so this is why you can imagine that a really well

controlled study on this would be very hard to carry out.

And I’m not really sure that it’s worth our tax dollars to

actually design and carry out a study like that,

because there would be so much individual variation in terms

of discipline in adhering to the feeding window,

whether or not people experience increases and drops in

blood glucose, how that impacts them,

whether or not they’re exercising,

it just becomes an infinite variable space, as we say,

in experimental science.

So you really have to determine that for you,

but I don’t think that we can fairly say that artificial

sweeteners break a fast.

I think that would be incorrect to say earlier,

we were talking about glucose disposal agents,

both behavioral and compound based things like metformin and

berberine. And in fact,

cinnamon is even a mild glucose disposal agent.

It can actually reduce blood glucose,

lemon and lime juice, believe it or not,

can lower blood glucose.

You may have experienced this before of eating something

very, very sweet and almost feeling kind of overwhelmed and

kind of poisoned by how sweet it is,

especially if you’re not accustomed to eating a lot of

sugary things.

One quick remedy for that is actually a half lime or a half

lemon squeezed into juice and drinking that just by virtue

of the taste and by virtue of the fact that it will reduce

blood glucose,

you’ll notice that that effect almost immediately

disappears. That’s not magic.

That’s the effects of acidity on blood glucose levels.

So there are a number of things that can adjust blood

glucose. They’re not necessarily disposal agents.

They’re not sweeping it out of the bloodstream in the same

way that berberine or metformin would,

or that high intensity exercise at the appropriate times of

day would,

but there is one particular thing that one can ingest that

can help manage psychologically and performance wise through

the fasting portion of the intermittent fasting and get you

to your feeding window. And that’s salt.

I’ve talked a little bit about this on the podcast before,

but because neurons use salt, sodium and potassium,

and magnesium,

the so-called electrolytes in order to perform their magic

of chemical and electrical signaling,

everything you do depends on chemical and electrical

signaling and all that chemical and electrical signaling

requires electrolytes in some form or another neurons run on

the passage of ions like sodium in and out of their cell

membranes, or I should say across their cell membranes,

to be accurate.

Many people find that the kind of lightheadedness,

the shakiness that’s accustomed with having slightly low

blood sugar can be offset by taking a half teaspoon or so of

sea salt,

or even just a tiny pinch of salt and putting into some

water and drinking it.

Some people find because of the glucose lowering effects of


that if they’re feeling kind of shaky and not well,

and they put some lemon juice into water and drink that it

drops their blood glucose further.

So there’s a common practice nowadays that’s discussed on

the internet of waking up,

drinking some water with some lime or lemon juice in it with

a little pinch of salt.

I think that little pinch of salt is a good idea.

What is it doing?

How is it offsetting all this?

Well, salt water actually has a mild effect as a glucose

disposal agent,

but it has a stabilizing effect on blood volume.

And so because sodium brings with it water and the so-called

osmolarity of your blood and your body depends on the salt

levels in your blood and brain and body.

Many people find that if they’re feeling shaky,

they’re feeling lightheaded.

They can’t concentrate.

They think they need sugar or food,

but what will actually remedy that is some salt.

And I know a number of people that have incorporated this

practice and have written to me and saying, oh, you know,

if I just take a little bit of salt and some water,

they may or may not include the lemon or lime juice.

They immediately feel better and find that it’s actually

quite straightforward to get out to that,

to wait until the feeding window kicks in.

This is especially true for people that are using caffeine

because when you ingest caffeine,

you actually excrete a lot of water has a diuretic effect.

And with that water goes salt.

So it actually causes you to excrete sodium.

Now the role of sodium in blood pressure and hypertension is,

you know, quite controversial science magazine,

one of the premier scientific journals out there had a

special issue all about salt some years ago,

talking about the research around hypertension, indeed,

people with chronic hypertension or high blood pressure or

very high blood pressure in particular should be wary of

ingesting too much sodium.

But for most people ingesting sodium,

provided they drink enough water and they don’t have chronic

hypertension or high blood pressure is actually beneficial.

Now that doesn’t mean you should be drinking seawater.

It doesn’t mean you should be overindulging in salt,

but many people find that they can manage their mental and

physical state and even feel really terrific,

real clarity of mind and really enjoy their fast when

they’re ingesting sufficient salt.

And all it requires really is a small pinch of salt,

ideally Himalayan or sea salt,

if you want to get fancy about it,

but table salt would be fine.

And just drinking that in some water,

maybe with lemon or lime juice to offset the taste a little

bit can really stabilize one’s jitters and can stabilize the


And you might also notice can offset that churning and

yearning and appetite where you can’t imagine going another

five minutes before eating something suddenly you feel okay.

And that has to do with a lot of the effects of blood

volume caused by ingesting salt in the appropriate amounts.

In other words, sometimes you think you need food,

but what you really need is salt and salt can make you feel

better immediately.

I’d like to mention two excellent zero cost resources.

If you’re going to explore time-restricted feeding,

or maybe if you already are doing time-restricted feeding,

I have no affiliation to either of these,

the first is the website that I mentioned before,

my circadian clock,

which is the website hosted by such in Panda and colleagues.

There are a lot of resources there where you can log your

food intake, get information about time-restricted feeding,

all the science, the ongoing studies, et cetera.

The other is the so-called zero app that makes it very easy

to mark when you’re beginning your feeding window.

And when you’re ending your feeding window,

and in so doing marking,

when you are beginning your fast and ending your fast,

or at least initiating the beginning of the unfed state,

as we could more accurately call it, it’s a terrific app.

I’ve used it from time to time.

I don’t tend to use it in an ongoing basis because I’m just

sort of used to eating at a particular time of day now,

but anytime I’ve shifted that window, for instance,

a few weeks ago,

I started moving that protein intake in my entire feeding

window earlier in the day.

And because that takes some attention on my part,

because I’m not used to doing that,

I’ve been using the zero app and I like it quite a lot.

It logs your progress and it gives you averages.

And you can see how many other people are fasting again,

totally zero cost.

I actually don’t know who owns that app,

but I think they’ve done an excellent job.

The interface is really terrific.

And as far as I know, it’s available for Apple and Android,

but it’s at least available for Apple phones,

which is the type of phone I happen to have.

So check those out.

My circadian clock, you just put that into Google,

you’ll find it.

And the zero app, both excellent zero cost resources.

In a moment,

I’d like to review the parameters of a ideal feeding

schedule for you and give you the variables that you can

plug into your lifestyle and your preferences.

There are a couple of things that I would place into the

category of frequently asked somewhat odd,

but still worthy of discussion.

For instance, people have asked,

will brushing your teeth with toothpaste, break your fast.

I think unless you’re swallowing the toothpaste, no.

Now, if you really want to run out and get a continuous

glucose monitor and brush your teeth,

and you can evaluate that, but no.

People have asked,

will a half glass of wine after dinner,

a couple hours after dinner, break your fast?


It absolutely will.

And it’s been demonstrated to do that based on the one gram

of sugar kind of eerie or scary effect that I talked about

before scary and eerie,

because it just seems like one gram of sugar.

How could it do that?

But these are metabolic processes and they are

very sensitive post meal.

A few months back,

I did an experiment wearing a continuous glucose monitor.

And I got a surprise when I discovered that going into a

sauna increases my blood glucose quite a bit.

It actually spikes it as high as a meal.

And then it tends to drop back down to baseline or even

slightly below baseline afterwards.

When I talk to people about this, somebody said,

oh, it’s got to be that the continuous glucose monitor was

getting disrupted by the heat in the sauna.

That’s actually not the case.

Turns out that when you go in a sauna,

because you dehydrate, you’re losing water.

I wasn’t drinking water and you’re dropping a lot of water.

The concentration of sugar in your blood actually goes up.

And I actually put these data out in a social media post on

Twitter and people were kind of shocked to see how much a

sauna can spike your blood glucose.

Now I do practice time-restricted feeding,

intermittent fasting.

I’m not super strict about it.

I use a kind of eight to 10 hour ish window either early in

the day or late in the day.

I saw this effect of the sauna personally,

the psychological and physical health effects of the sauna

are valuable enough to me that I continue to use it.

I just not concerned about this increase in blood glucose to

the extent that I’m going to eliminate sauna.

I like to use the sauna three or four times a week before


So I’ll use it an hour or two before sleep.

And yes, indeed,

it creates this big spike in blood glucose that then drops

based on change in the concentration of blood sugar.

I’m just not going to worry about it.

Now, if you’re concerned about blood glucose spikes,

then you might be worried about it.

But in my case,

it was one of those things where it was interesting and it

was worthy of discussion, I thought,

because it was somewhat surprising to me,

although it makes perfect sense why this would be the case,

but at the end of the day, literally,

it just makes sense for me to get in the sauna.

Okay. So now you’ve heard a lot of science.

You’ve heard a lot of examples,

even a few anecdotes,

and let’s come up with the ideal intermittent fasting,

AKA time-restricted feeding schedule for you.

And when I say ideal,

I mean, what are the variables that are negotiable?

What are the ones that are non-negotiable?

What is ideal for you will depend on the context of your

life and what you are willing to do consistently.

So first of all,

we established based on the discussion with Sachin,

who is truly the premier world expert in this area,

who knows the animal and human scientific literature better

than anybody has written this incredible review.

And for whom I consulted that you do not want to ingest food

for at least,

I want to emphasize at least 60 minutes post waking up.

Second, you want to avoid ingesting any food

of any kind, even one gram of sugar.

Remember, this is the ideal.

One gram of sugar even would be too much for the two to

three hours prior to bedtime.

He also mentioned, ideally,

you are spending eight hours in bed.

I didn’t tell you that earlier. I saved that for now,

but ideally you’re sleeping that entire eight hours,

but simply by being in bed for that eight hours and avoiding

food after waking for an hour and before bed for two to three

hours, you’re starting to build out the duration of this

fasted period.

Remember that the sleep related fasting is particularly

important for the health benefits of time restricted feeding.

Again, the sleep related fasting is especially important

because of all the cellular repair processes that occur in

the liver, in the gut, in the microbiome,

in the brain, all over the body.

And because of the way that that coordinates the expression

of the clock genes that are then going to wick out and have

many other positive effects on health,

including weight and fat loss.

But in addition to that liver health, et cetera,

an eight hour feeding window as a target seems to be the

best target feeding window,

at least by my read of the literature and in discussing it

with such in shorter feeding windows of four to six hours

tend to lead to overeating and potentially increases in


One meal per day type eating do not seem to do that,

but those are special cases in that most people can’t adhere

to a one meal per day type schedule,

at least not on a regular basis.

And it’s not very compatible with most social schedules.

Although some people may be able to adhere to that in a

straightforward way,

but there aren’t any robust studies exploring the advantages

of one meal per day.

So if you feel there are advantages of one meal per day for

you, as opposed to an eight hour feeding window,

well then by all means use a one meal per day approach or

use a four to six hour feeding window and just make sure you

don’t overeat in that window.

Remember that most people tend to not adhere to the eight

hour feeding window.

They say eight hours,

but they tend to eat outside of the eight hours a little bit

on each side.

So if your goal is a 10 hour feeding window,

you might want to set it to nine hours or eight hours.

If your goal is six hours,

you might want to set it to seven or eight hours.

And this is simply based by, I shouldn’t say simply,

this is based on thousands,

if not tens of thousands of human subject data points that

Satchin and colleagues have collected.

Regular placement of the eating window or feeding window

every 24 hours is important.

You don’t have to be absolutely rigid and neurotic about


but you don’t want it sliding around on the weekend so that

it’s starting two hours later and ending two hours later a

couple of days a week,

because then you start to offset many of the positive health

effects that have been demonstrated for time restricted


Remember if you eat your food within a certain feeding


shifts by a couple hours,

it is effectively like jet lagging your system.

It is effectively like traveling a couple of time zones over

eating there for a few days and coming back when in fact

you’re not traveling.

And that’s because of the way that food adjusts the

circadian clock genes.

Now you can offset some of that through the use of light.

And I’ve talked extensively about how to use light in

previous podcasts, but again,

early morning and all day bright light exposure as safely as

you can, ideally from sunlight,

not through a window, et cetera,

avoiding bright light in the middle of the night,

extremely important for mood offsetting,

metabolic dysfunction, et cetera.

Not incidentally such in his early work was he was one of

the three co-discoverers of the cells in the eye,

the so-called melanopsin cells that set the central

circadian clock.

So he was a pioneer in that field,

which led him to be a pioneer in this field and so on.

When should that eight hour window be placed within each 24

hour cycle?

Well, let’s talk about ideal ideal.

If you really want to maximize all the health benefits of

time, restricted feeding,

you need to extend the fast around sleep on both sides.

You would place it smack dab in the middle of the day.

It would be a schedule in which you started eating for

instance, at 10 AM and you stopped eating at 6 PM and

absolutely dreadful schedule for anyone that wants to have

some semblance of a normal life.

In my opinion,

it’s not really compatible with most schedules,

although some people might be able to do it.

Maybe you and your family or your friends,

you’re, you know,

you’re eating a late breakfast or a,

and then you’re having a latest lunch around 2 PM.

And then you have dinner at six and then assuming that you

go to bed around nine 30 or 10 PM,

that is going to extract the maximum amount of weight

related body fat related metabolic factor related aspects of

time, restricted feeding.

Some people tend to fall into a category where they do best

placing that feeding window later in the day and provided it

doesn’t run too close to your sleep.

Remember you need a two or three hour buffer before your

sleep where you’re not ingesting anything.

That’s in order to extract the benefits of time,

restricted feeding.

Well then starting your feeding window at 12 PM and ending

at 8 PM plus or minus half an hour or so day-to-day seems

like a perfectly reasonable schedule for some people

starting at 2 PM and ending at 10 PM will be that schedule.

Of course,

you have to take into consideration when you exercise,

if you exercise, for instance,

I like to exercise early in the day,

if I run or if I do some moderate or light intensity

exercise, regardless of what type of exercise it is,

I have no trouble waiting until my feeding window kicks in

around noon or even 2 PM.

But if I do high intensity weight training, for instance,

early in the day,

or if I run sprints and I do that at 7 AM or 8 AM by 11 AM,

I am very, very hungry.

And it’s hard for me to do other things,

concentrate, et cetera.

Now I’m not neurotic about my feeding window.

As I mentioned before,

I kind of let it expand and contract a bit around the eight

hour mark and feel perfectly free to do that too.

We’re talking here in, in ideals,

not in necessarily practicals,

but other people find that they’re very hungry when they

wake up early in the day.

If you’re one of these people,

or you’re somebody who really is trying to emphasize

hypertrophy or maintenance of muscle,

then it does seem that ingesting protein early in the day is

beneficial that it can be more readily converted into

muscle tissue.

And this has been demonstrated in at least one study.

There’s another study underway.

That’s exploring this further for people that are really,

really interested in hypertrophy and building muscle.


then time restricted feeding is usually not the way they go.

I mean, let’s be honest.

There are many people out there who are eating four or more

meals per day.

And they’re doing that from 7 AM until 8 PM.

I realized that not everybody is overweight.

There is an obesity crisis.

Indeed, you know,

the percentage of obesity and non-alcoholic fatty liver

disease is just cosmic through the roof,

at least in this country and in other countries as well,

this country, me in the U S but other countries as well.

But there are of course,

people that are trying to gain weight or who don’t want to

lose weight or who are trying to maximize physical

performance or hypertrophy or things of that sort.

And so of course time restricted feeding for them might be

as long as I’m awake, I’m eating.

And I, you know,

tip my hat to those people and just say, you know,

provided you understand what you’re doing and the burden

that that places on some of the other processes in your

body, if that’s right for you,

then by all means pursue that.

Another thing that we can add to this summary or key points

related to time restricted feeding is the use of glucose

disposal agents and or behaviors.

If you find that you’ve eaten too close to a period of time

in which you would prefer to be fasting,

that’s when a 30 minute brisk walk or even modest walk

after eating can be beneficial.

Ingesting some lemon juice or lime juice can help lower

blood glucose somewhat.

And then there are the things like metformin and berberine.

There are even some supplements out there that combine

things like berberine cinnamon,

which can lower blood glucose and things like chromium and

things that have a mild effect on blood glucose,

but berberine and metformin are very high potency glucose

disposal agents.

And I mentioned earlier why you would want to approach those

with the appropriate level of caution and figure out the

dosages for you.

And for some people,

the dosages will be zero milligrams is going to be ideal.

And then of course we discussed how making sure that you’re

ingesting enough fluids in particular water and salt,

especially if you’re using caffeine in order to increase

your levels of alertness,

regardless of where that caffeine source comes from coffee

tea or otherwise that can cause the excretion of sodium and

can lead to a kind of shakiness,

a lightheadedness and the feelings of hunger that may or may

not be related to blood glucose.

Some people genuinely need to eat.

I certainly would not want to see people getting

hypoglycemic to the point where it’s dangerous.

Certainly if you are diabetic, you, and in fact,

for all people,

you should consult with your physician when exploring any

major changes to diet or additions or subtractions of

anything, including supplementation.

But for most people maintaining relatively low to modest

blood glucose levels is going to be pretty healthy and will

allow all the positive effects of intermittent fasting to


And when you find that reaching that start to the feeding

window is challenging that ingesting sodium can often

stabilize your system mentally and physically and allow

you to reach that window often painlessly.

And then as a final point, as I mentioned earlier,

provided that they are consumed in low,

no or modest amounts,

artificial sweeteners or plant-based non-sugar,

non-caloric sweeteners don’t seem to really impact blood

glucose to the extent that it would quote unquote,

take you out of your fast.

But that like fat fasting is something that’s going to be

highly individual and that you’re going to have to

experiment with for yourself and being able to recognize

when you’re in a fast and when you’re out of a fast at a

subjective level and not constantly having to measure your

blood glucose or do things of that sort can be beneficial.

And I think if you watch for the feelings associated with

eating and post-eating foods of different kinds and

different amounts,

and you watch for the feelings associated with being fasted

for long periods of time or short periods of time of having

gotten sufficient sunlight of having trained hard or not

trained hard earlier that day, et cetera,

you can do the most important thing,

which is to start to learn, to evaluate your own system,

to run simple,

safe experiments on your system in a way that allows you to

really establish the ideal nutrition schedule for you,

whether it be time-restricted feeding,

AKA intermittent fasting or some other nutritional plan.

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I know we covered a lot of information today.

I hope you learned a lot about time-restricted feeding.

I hope you learned a lot about metabolism and energy and

health and how,

when you eat is as important as what you eat and last,

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thank you for your interest in science.

Thank you.

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