Huberman Lab - How Foods and Nutrients Control Our Moods

Welcome to the Huberman Lab Podcast,

where we discuss science

and science-based tools for everyday life.

My name is Andrew Huberman,

and I’m a professor of neurobiology and ophthalmology

at Stanford School of Medicine.

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,

I’d like to thank the sponsors of today’s podcast.

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I’ve done a couple of episodes now

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Today, we’re talking all about emotions.

Emotions are central to our entire experience of life.

Whether or not we’re happy or sad or depressed or angry

is our life experience.

And yet, I think with all the importance

that we’ve placed on emotions,

very few people actually understand

how emotions arise in our brain and body.

And I mentioned brain and body,

because as you’ll see today,

emotions really capture the brain-body relationship.

We cannot say that emotions arise

just from what happens in our head.

It also involves events, biological events,

chemical events within our body.

The other thing about emotions

is that there’s no real agreement

as to what’s a good emotion or a bad emotion.

Today, we’re going to talk about the biology

of the chemicals and pathways that give rise to emotions.

And I’m going to equip you with several, if not many, tools

that will allow you to regulate and change

and steer your emotions should you want,

but not using the typical advice.

You know, everyone’s probably heard of this thing.

Oh, you know, if you’re feeling depressed, just smile.

You know, it’s impossible to be depressed while smiling.

Look, if that were true,

we wouldn’t have any depressed people,

because depressed people don’t want to be depressed.

And it is not the case that simply smiling

will reverse depression or sadness.

And it’s simply not the case

that smiling can inhibit sadness.

It just doesn’t work that way.

However, it is the case that certain things

that are happening in our body

influence how our brain functions

and the chemicals that are released.

And today, we’re going to talk a lot

about how the brain and body interact

to create these things called emotions

in the context of food and nutrition.

And the reason we’re doing that

is not because I am beating the drum

about particular diet regimens or anything.

In fact, I’m not going to do any of that.

What I’m going to do is I’m going to review

some of the most important scientific data

that point to how ingesting certain nutrients,

both macronutrients like proteins, fats, and carbohydrates,

as well as micronutrients,

can impact the chemicals in our brain

that give rise to the feelings of being happy

or sad or sleepy or alert when you want to be sleepy

or sleepy when you want to be alert.

So this is sure to be a broad discussion,

and yet we’re going to get very specific

about what emotions are, how they arise in the body,

tools that one can use

in order to better control their emotions,

tools that people can use to, believe it or not,

feel happier or feel calmer.

And that’s because in the last 20 years or so,

there’s been an explosion of scientific studies

exploring how the brain and body interact

to support certain neurochemicals

that give us these feelings of being alert and happy

or depressed or certain that our life

is going to be terrible

or certain that our life is going to be great.

So as mysterious as all that might sound

and confusing as all that might sound,

we’re going to make it very clear today.

And you’re going to come away from this conversation

with a lot of tools that you can act on immediately.

And those tools are grounded in scientific data.

We are going to provide links to several of the studies,

and I’m going to mention several of those studies

as we go along.

But overall, the goal today is for you to understand

how moods and emotions arise

and the different pathways in your brain and body

that allow them to happen

and how you can use those pathways to change those emotions

and the tools that you can rely on in very specific ways

to shift from being, say, slightly depressed

to feeling happier.

There actually are ways to do that,

or from feeling too alert and anxious to feeling calmer.

And these are tools that are distinct

from the tools I’ve talked about in previous episodes.

The discussion around emotions has a long and rich history,

going back to Darwin and even long before Darwin.

This is a conversation that philosophers and scientists

have been having for hundreds, if not thousands of years.

The idea that Darwin put forth

and that was really attractive for about the last 100 years

was that emotions are universal

and that some of the facial expressions

around emotion are universal.

And other people have capitalized on that idea.

And to some extent, it’s true.

I mean, I think that the two most robust examples of that

would be when we see something or we smell something

or we taste something that we like,

there does tend to be a postural leaning in.

We tend to inhale air at that time.

We tend to bring in more

of whatever chemical substance is there.

So we tend to do these mms

and kind of lean in closer to things

that are attractive to us.

And when we see and experience things that we don’t like,

sometimes it’s a mild aversion.

We just kind of lean back or look away.

Other times, it’s an intense aversion of disgust

and we tend to cringe our face.

We tend to avoid inhaling any of the chemicals.

This probably has roots in ancient biological mechanisms

that are to prevent us from ingesting things

that are bad for us, chemical compounds

and tastes that might be poisonous.

So much of the foundation of any discussion about emotion

has to center around this kind of push-pull

of attraction to things or aversion from things.

Now, that’s a very basic way of thinking about emotions.

But if you think about it,

it works for a lot of different circumstances.

And in the brain,

everywhere from the deep circuits of the brain

to the more kind of what we call higher order

revolve centers of the brain,

we have this push-pull thing.

We’re either, in a previous episode, I talked about go,

the circuits that allow you to emphasize action

and then no-go circuits,

the circuits in the basal ganglia

that allow you to de-emphasize action and prevent action.

We talked about how that’s a push-pull.

So aversion and attraction is a push-pull too.

Delight or happiness or excitement

are attractions to certain things and ideas,

songs, people, places, foods.

Aversion is a leaning out.

It’s a disgust.

It’s an avoidance.

And so we can break down the discussion about emotions

into these simpler versions of themselves.

But at the core of that,

of attraction or aversion is an important theme

that you might realize already,

but most people tend to overlook,

which is that there’s an action there.

You’re either moving forward

or you’re moving away from something.

And anytime you’re talking about action

in the nervous system,

you’re talking about motor behaviors.

You’re talking about literally the contraction of muscles

to move you toward or away from things.

And anytime you’re talking about nerve to muscle and action,

you’re talking about the brain and the body

because the brain can’t move itself.

The brain has a body so that the organism can move.

And the body has a brain so that the organism, you,

can move toward or away from things

that you deem to be good or bad for you.

Now, some of these things that we’re attracted to

and some of them that we avoid

are what we call innate or hardwired.

You know, when we taste bitter compounds,

I’m not talking about bitter,

like you like a little bit of bitters in your drink

or something like that, but really bitter compounds,

we tend to avoid those

because they’re associated with poisons.

When we taste things that are sweet or that are savory,

we tend to pursue more of those.

We tend to lean toward those, so to speak.

And we tend to not avoid them.

So there are circuits in the brain for aversion

and for attraction toward things,

and the body is governing a lot of that.

And so immediately in this conversation,

I want to raise an important point,

which is about a nerve pathway

that many, many people have heard of

that gets discussed all the time

and that is one of the most kind of oversold

for the wrong reasons and undersold, unfortunately,

for its real power, which is the vagus nerve.

So the vagus nerve is one, not the only,

but one way in which our brain and body are connected

and regulates our emotional states.

Now, many of you have probably heard

about polyvagal theory.

I’m going to talk about this today.

Polyvagal theory was popularized by Stephen Porges.

And it’s an interesting theory.

Certain aspects of it, frankly, hold up to the science.

Some of it doesn’t.

And I’m going to discuss all of that today.

A lot of the vagus and the excitement about the vagus,

V-A-G-U-S, is because it somehow got into the mind

of the public that the vagus is involved

in calming us down.

So what is the vagus nerve?

Okay, we’re going to make this really simple.

In particular, for those that are just listening,

you can just imagine this.

For those of you that are watching,

I’ll point to the various areas.

But basically, vagus is the 10th cranial nerve,

which basically means that the neurons,

the control center of each of those neurons in the vagus,

lives just kind of near the neck, right?

And a branch of the vagus goes into the brain.

They send a little wire into the brain.

The other branch goes into the periphery,

but not just the gut.

It goes into the stomach, the intestines, the heart,

the lungs, and the immune system.

So this vagus nerve is incredible

because it’s taking information from the body,

and it has two directions.

The first is what we call sensory.

So it’s sensing things that are happening

in the gut, in the lungs.

Everything, for example, in the lungs,

when our lungs are distended,

the vagus nerve senses that

and sends that information up into the brain.

It also can sense things in the gut,

like how distended or empty your stomach happens to be.

It can sense heart rate.

It can sense your immune system,

whether or not you have bacteria

or things invading you in your body.

So it sends that information up to the brain.

So it’s a two-way street,

and sensory information is going up to the brain.

That’s all vagus.

So it’s like a superhighway.

Sensory information going one way,

and then the other direction is motor control.

So the vagus is not just for sensing things.

It’s actually for controlling things.

It’s got a sensory pathway and a motor pathway.

So that’s the first thing I think everyone should know

about the vagus.

In fact, it’s so important

that I feel like this is as important

as people knowing that walking involves flexors

and extensors.

And if you don’t think that’s important,

it’s as important as walking, frankly,

because the vagus is the way in which you can govern

the brain-body connection

and in which you can steer various aspects

of your mood and wellbeing.

But most people just don’t understand how to use it.

So first you got to understand what it is.

So you’ve got sensory information

coming from all these different organs of the body

up to the brain.

You got motor information going from the brain

back to the body.

And so you’ve got this superhighway within you.

Now, what actually regulates the vagus?

Oftentimes you’ll hear things like,

oh, you know, this particular behavior,

you know, rubbing your face at a particular location

or breathing in a particular way,

or, you know, a warm bath or something

stimulates the vagus.

Well, right now I want everyone to know that,

quote unquote, stimulating the vagus, broadly speaking,

is a terrible way to think about the vagus.

Because did you know what?

If you have a contaminant inside your body,

the vagus senses that and projects that information

to your brain and you start to generate a fever.

You start to try and kill that contaminant in your body.

So I don’t know that you want to stimulate the vagus

just as like a general theme.

Today, we’re going to get specific

about how you can activate particular circuits,

certain pathways from certain organs to the brain

in order to feel better or relieve certain conditions.

But you certainly don’t want to just stimulate the vagus.

Now, excitement about the vagus in part

is because of what quite honestly

was a fairly pioneering theory about the vagus,

which is this polyvagal theory.

So polyvagal, the word poly means many,

is cool because it acknowledges

that the vagus has a lot of different branches.

It’s not just one thing.

And so I really like that.

I like the naming polyvagal.

The idea that Porras put forward

was that there’s a dorsal vagus,

which is kind of runs the back of the spinal cord,

which is involved in alertness and activation

and kind of fight or flight type stuff.

And that there’s a ventral pathway.

And that that’s involved in more kind of empathic behaviors.

That is not quite in agreement with the modern anatomy,

but he was doing the best with what he had at the time.

So, okay.

The problem I have with the polyvagal theory

is the way that it’s discussed.

People often say, oh, you know,

if your dorsal vagus is too active,

then you tend to be someone who’s a little too keyed up.

And people who are kind of in a state of freeze

or kind of flaccid and kind of, you know,

just not really active and they’re just lethargic.

Well, then that pathway is hypoactive.

It should be more active.

So, there are a lot of theories

about how psychology maps onto the vagus

that as far as I know, don’t map to any real physiology.

Now, the other problem with this kind of

the way that the polyvagal theory is discussed,

probably not by the real experts,

but by a lot of people is that people start to diagnose

different psychological and physical manifestations

through the vagus.

They would say things like, oh, you know,

this person is hyperflexible at the joints

and therefore their dorsal vagus isn’t active enough

or something like that.

And it’s really kind of gone way outside the lane lines.

So, today we’re going to clean up a lot of that.

Let’s make it really simple

about how the vagus actually works,

at least as we understand it today in 2021.

First of all, as I mentioned, you have sensory information.

The same way that you detect light with your eyes

or you hear sounds with your ears,

you have sensors in your gut

that sense how full or empty your gut is.

It can also sense how acidic your gut is.

It can sense various things within your gut.

Your heart is doing the same.

It’s informing the brain how fast your heart is beating,

how full your lungs are has been communicated,

and then the status of your immune system.

So, the way to think about the vagus

is the same way I would think about the eyes.

The eyes are looking at colors, they’re looking at motion,

they’re looking how bright it is.

And each one of those things, those features,

is telling the brain something different

so the brain can decide when to be awake or asleep,

whether or not it’s looking at somebody

attractive or unattractive.

The vagus nerve is also analyzing many features

within the body and informing the brain

of how to feel about that and what to do.

So, a really good example that I think is an exciting one

is as it relates to sugar.

So, we all know that sweet things generally taste good.

I’m not particularly a fan of very sweet things.

You know, I’d much rather have, you know,

cheese or pizza or hamburger or steak.

I like savory fatty foods, but I do like sweet foods.

And most people find sweet foods to be attractive.

They want them.

They might or they might not be able to regulate

their behavior around them, but they want them.

And what’s really interesting is that for hundreds of years,

people have thought that that’s because of the way

that sweet foods taste.

So, that makes sense, right?

You eat something, it tastes sweet.

You want more of it.

Well, it turns out that it’s much more interesting

than that.

When you eat something sweet, within your stomach,

you have cells, neurons, that sense the presence

of sugary foods independent of their taste

and signal to the brain.

So, those sensors, those neurons send information

up the vagus to your brain,

goes through a series of stations,

and then you release dopamine.

This molecule that makes you want more of whatever it is

that you just ingested.

In fact, this pathway is so powerful

that they’ve done experiments where they completely numb

all the taste and feeling in somebody’s mouth.

They’re blindfolded, so they don’t know what they’re eating.

And they’re eating a food that’s either sugary

or not sugary.

And what they find is that even though people can’t taste

the sugary food, they crave more of the food

that contains sugar because of the sensors in the gut

that sense sugar.

So, to put this differently,

you actually have sensors within your body

that make you crave sugar independent

of the sweet taste of those things.

Now, that’s incredible.

And what it does, and what it tells us,

is that we have circuits in our body

that are driving us towards certain behaviors

and making us feel good, even though we can’t perceive them.

Now, for those of you that are really interested

in gut intuition and kind of gut feelings,

this is a gut feeling,

except this is a chemical gut feeling.

This is a particular set of neurons

detecting that something in your body

has a particular feature, in this case,

the presence of sugars, and sending information

to the brain essentially to control your behavior.

And I find this remarkable because what it means

is that what we call attractive isn’t always coming

from our thoughts about that,

or our feelings, or even our perception.

We are drawn to particular foods,

and we’re drawn perhaps also to particular people,

places, and other things because of information

that’s coming from our body.

And we’re going to talk about

what one can do with this information.

I know many people are thoughtful

or concerned about sugars these days,

thinking, you know, we all ingest too much sugar.

There’s sugar snuck into all the things we eat.

And indeed, that’s true.

I mean, this should completely reframe

the way that we think about

the sort of so-called hidden sugars in foods.

What this means is that even if a food is very savory,

like a piece of pizza, or a piece of bread,

or even like a salad dressing,

if there’s sugar snuck into that and you can’t taste it,

you will still crave more of that thing

without knowing that you crave it because it has sugar.

In other words, you might find yourself

wanting certain foods

and not knowing why you want those foods.

So I find this to be a fascinating aspect

of our biology.

And yes, it relates to mood and emotion.

And we’ll talk about how that is in a moment.

So let’s just back up a bit and ask the question,

why do we eat certain things?

And why do certain foods make us feel good

and other foods actually make us feel anxious?

I think some people may be familiar with this.

Other people might not.

But most people don’t realize that as you approach eating,

there’s an anxiety associated with that.

It’s an alertness.

Remember in the previous discussions,

or even if you don’t and you haven’t seen those,

all of your moods and feelings of wellbeing

are anchored on this continuum of alertness versus calmness.

And we hear so often about rest and digest,

that, oh, after we eat, we feel really nice and full,

hopefully comfortably full and not too full.

And we’re relaxing and we feel satiated.

It’s associated with serotonin, this molecule of satiation.

That’s all true.

But what most people don’t know

is that there’s an area of the hypothalamus,

so deep in the brain,

kind of in the middle deep portion of the brain,

called the lateral hypothalamus.

And the lateral hypothalamus is really interesting

because it controls feeding, but it inhibits feeding it.

It stops us from feeding.

And there’s another area in the brain.

If you want names, I’ll give them to you.

If you don’t want names, just ignore them,

delete them from your memory and awareness,

called the locus coeruleus.

Now the locus coeruleus sits back further in the brainstem

and it releases norepinephrine,

which is essentially adrenaline and makes us feel alert.

Now locus coeruleus has a lot of different functions

in the brain, but when we are going to eat,

let’s say we walk into a restaurant,

we sit down or we’re preparing a meal,

locus coeruleus is known to release noradrenaline

in the brain.

It’s creating a kind of alertness.

This has ancient utility, but it’s creating this alertness.

And for many people, they experience that

as they approach food, as stress, as anxiety.

But what’s interesting is that as we approach food,

locus coeruleus is releasing all these molecules

that make us feel more anxious and alert.

Sometimes it’s felt as excitement,

and that has probably to do

with how we feel about food generally.

Are we happy with our relationship to food?

Are we trying to restrict our relationship to food?

Are people coming over for dinner?

All that will play in, of course,

but there’s a certain stress and anxiety

on approach to food.

And as we approach food and we feel that anxiety,

locus coeruleus activates the lateral hypothalamus

in a way that inhibits feeding,

that makes us not want to eat.

So a lot of people who have kind of pre-meal anxiety

or anxiety around food,

and they can’t seem to just calm down and have a good meal

to access that later rest and digest,

a lot of that is because of this heightened stress

upon approach to food.

And a lot of the tools that are out there,

both for eating disorders

and for just kind of the general public

who isn’t suffering from eating disorders,

things like mindfulness around meals.

They always tell you,

you should never eat when stressed.

I’m sorry, but my life is not organized

in a way that I can’t do that.

I would never eat, right?

Because I eat when I’m awake,

and I don’t know if I’m stressed,

but I don’t think I am,

but I tend to run around a lot during the day.

I don’t generally take time

to do two or three deep breaths before I eat.

I generally will just keep, will eat.

That can be healthy or unhealthy

depending on the quality of your digestion.

I think using digestion as a guide is good,

but a lot of people aren’t aware

that this interaction between locus coeruleus

and lateral hypothalamus is a basic mechanism

where we are supposed to get a little bit alert

and anxious around mealtime.

And then as we eat,

the mechanisms for calming and satiation

are supposed to kick in.

And those mechanisms involve,

as I mentioned earlier, two things.

One is how things taste.

Digestion starts in the mouth, of course.

We taste our food.

Everyone tells us we should chew our food more.

Yes, that can improve digestion.

We’re not supposed to drink too many fluids as we eat.

That’s true too.

But a lot of how we feel while we eat

and after we eat is because of this vagus sensing

of what’s in our gut.

It’s sending information all the time.

Is there sugar?

Are there fats?

Are there contaminants?

There are a lot of information,

these so-called parallel pathways

that are going up into our brain

that regulate whether or not

we want to eat more of something or not.

And there are accelerators,

things that make us want to eat more,

like sugar and fats,

because those are nutrient dense

and they helps generally, at least in the short term,

support the survival of animals,

but also amino acids.

And this is very important.

There are a lot of data,

but much of what comes from the data

on what people eat and how much they eat

is from a subconscious detection

of how many amino acids and what the array,

meaning the constellation of amino acids is in a given food.

And it’s fair to say that the sum total of these studies

point in a direction where people will basically eat,

not until their stomach is full,

but until the brain perceives

that they have adequate intake of amino acids.

Now, this is a conversation that comes up

in the context of the meat only, the keto,

the kind of zone diet, the Mediterranean diet,

the vegan diet.

I’m largely going to ignore the kind of strict camps today.

I will talk a little bit about it

because I think each one of them

actually taps into something important

about this brain body relationship

that the other ones don’t.

But I don’t want to get into a discussion

about the ethics of different foods

of animal-based or non-animal-based

because that’s not the topic today.

It’s really about nutrient sensing and amino acid sensing.

So we generally will eat until our gut tells our brain

that we have adequate amounts of these amino acids.

Amino acids, of course, are important

because they are the building blocks of, sure,

muscle and the other things in our body that need repair.

But what most people don’t realize

is that amino acids are what the neurochemicals

in the brain are made from.

Now, this is vitally important, okay?

So we’ve heard dopamine is this molecule

that makes you feel good.

Actually, dopamine is a molecule that makes you feel good.

It’s released within the brain

and it does feel very good when you have dopamine release.

Dopamine release is caused by surprise, excitement,

events that you’re looking forward to

and that turn out well.

It is inhibited by events you’re looking forward to,

that don’t work out.

When someone says they’re going to call

that you’re really, really excited to talk to

and then they don’t.

Or you thought a movie was going to be really great

and it’s not.

Or you expect a meal to be really delicious

and it’s kind of eh.

And we actually, there’s a name for that.

It’s called reward prediction error.

So if, and you can actually use this

in the context of meals and plans

in a way that’s very useful with yourself

and people you know.

Essentially, if you expect something to be really terrific,

it really does place a higher expectation

at the chemical level.

So if you don’t get as much dopamine

as you’re expecting from something,

so you hear about a really great restaurant

or a place that has a really,

in my case, I wouldn’t call it an addiction.

I would call it more of an affliction for croissants.

The best vegetable, of course, is the croissant.

And I get really excited about the fact

that someone will tell me, oh, there’s this place

and they have incredible croissants.

You got to go there.

So I get really excited and I’ll go.

And just them telling me

that it’s going to be really terrific raises an expectation,

a dopamine expectation.

And unless those croissants are amazing,

chances are I’m going to experience them as less good,

less satisfying.

I will truly release less dopamine

than I would had they just said,

oh yeah, I think that there are croissants down the street

or if I just tried one at random.

And that’s because of this reward prediction error.

Your expectation of something releases dopamine

and the actual event releases dopamine.

And if the event related dopamine

does not exceed the expectation or at least match it,

there’s a much higher tendency

that you won’t pursue that thing again.

So dopamine is really powerful

and it’s not just the molecule of reward,

it is the molecule of desire.

It’s the molecule of wanting,

not just the molecule of having.

And a book, since people often ask for book recommendations,

I don’t know the author personally, but I love the book.

It’s called The Molecule of More.

It’s a terrific book.

I wish I had written it, frankly.

But if you want to learn more about dopamine,

reward prediction error,

and how dopamine regulates various aspects

of your emotional and motivational life,

it’s a terrific read.

Dopamine is what’s going to lead us

to want to eat more of something

or to not want more of something.

Because dopamine really is about craving.

It’s about motivation and it’s about desire.

And as I mentioned, these amino acid sensors in our gut

are detecting how many amino acids,

but they’re also detecting which amino acids.

And there’s a particular amino acid called L-tyrosine,

which comes from food.

You can look up online which foods contain L-tyrosine.

It is in meats, it is in nuts,

it is also in some plant-based foods.

L-tyrosine is the precursor to a couple other molecules

like L-DOPA, et cetera, that make dopamine.

And so there’s a misconception out there

that most of the serotonin is in our gut

and most of the dopamine is in our gut

and therefore our mood is in our gut.

That’s not quite the way it works, okay?

We’ll talk about serotonin in a moment,

but dopamine is synthesized

from the amino acids that you eat.

However, the dopamine neurons that give rise

to these feelings of good or wanting more

or desire and motivation, those reside in the brain.

So we don’t want to get too confused.

We want to respect and honor the power of the gut

and this vagal pathway,

but it’s really neurons within your brain

that drive the pursuit and decision-making.

So what does this mean?

Well, some people make too little dopamine.

Some people make so little dopamine

that they need prescription dopamine.

They need L-DOPA.

People with Parkinson’s take L-DOPA

and other compounds to increase dopamine

because Parkinson’s is associated

with deficits in movement.

It starts as a tremor.

Actually starts as some other things that are interesting.

We’ll talk about in a moment,

but Parkinson’s is a depression.

It’s a blunting of motivation and mood and affect

and it’s a tremor.

And then eventually in severe conditions,

it’s challenges in speaking and walking.

So some famous examples would be Muhammad Ali,

Michael J. Fox, the great boxing trainer, Freddie Roach.

These people have Parkinson’s

and they, at least later in their life,

had challenges speaking.

Now, it’s not just fighters that develop Parkinson’s.

As far as I know, Michael J. Fox wasn’t a fighter.

People can develop Parkinson’s

and Parkinson’s is a depletion

of dopamine neurons in the brain.

And it’s not just movement challenges,

it’s challenges with mood.

Now, hopefully most of you, all of you,

don’t have Parkinson’s,

but it’s clear that dietary L-tyrosine

supports the healthy production of things like dopamine

and as well as other factors within the brain.

Now, some people immediately ask,

well, should I supplement L-tyrosine?

So let’s just talk about that

because that’s going to come up.

Full disclosure, I sometimes take L-tyrosine.

I’m not taking it right now, but I take it only occasionally.

You can buy this in capsule form.

It does increase kind of mood and elevation and alertness.

It is over the counter.

You have to check with your doctor.

I’m not responsible for your healthcare

and I’m not a doctor.

Whether or not it’s safe for you.

People with preexisting hyper-dopaminergic conditions

like mania should probably not take L-tyrosine.

The other thing about taking L-tyrosine

is there is a crash, okay?

It’s not a massive crash if you take it at appropriate doses

and it’s right for you,

but it can produce a crash and a lethargy

and a kind of brain fog after the next day or so.

And so L-tyrosine, however,

can be ingested through foods or through supplementation

to increase dopamine levels.

That’s well-known.

Taking chronically, however,

it can disrupt those dopamine pathways.

Now, there are other drugs that will increase L-tyrosine

and dopamine as well,

but those are severe enough

that they generally tend to have addictive properties.

So things like methamphetamine,

things like cocaine are terrible

because they really ramp up the dopamine system so much

that people really can’t achieve dopamine release

through any other mechanisms.

But food and the ingestion of L-tyrosine

has a profound effect on our levels of dopamine.

It takes a little while,

but that really will impact level of mood.

Certain antidepressants fall into the category

of dopaminergic antidepressants.

One of the most famous ones, of course, is Welbutrin.

Welbutrin was developed

because a lot of the other antidepressants

tend to make people feel kind of lethargic

or they had side effect profiles that people didn’t like.

So they developed this thing

that the generic name is different,

but it’s generally called Welbutrin.

Welbutrin activates dopamine and epinephrine,

which is a substrate of dopamine,

and both of those are involved in motivation

and alertness and effort.

So you might say, wow, this sounds like a great drug.

However, this drug, the side effect profile

tends to be the things that are associated

with elevated mood and alertness.

So this isn’t like taking some L-tyrosine,

this isn’t like eating some tyrosine-rich foods.

This is really a much greater release

of dopamine and epinephrine,

and it increases things like anxiety,

sweating, the pupils dilate.

It has certain effects on,

in particular, people with epilepsy.

It’s been used somewhat successfully for smoking cessation,

but again, it’s not for everybody,

and I’m not here to encourage the use of these things.

I’m just describing the biology and the rationale

for why these drugs were developed.

So let’s back up a second.

Let’s just kind of take stock of where we’re at.

We have a brain-body connection.

There are many of them,

but one of the main ones is the vagus nerve.

The vagus collects information about a lot of things,

breathing, heart rate,

stuff that’s happening in the gut, et cetera,

and gut, by the way, includes the stomach and the intestines,

sends that information up to the brain.

The brain is using that information

to decide one of two things,

move toward something or move away.

It can also pause,

but essentially pausing is not moving toward.

So that’s the dopamine pathway,

and foods rich in L-tyrosine

generally give us an elevated mood

and make us want to do more of whatever it is

that we happen to be doing, as well as other things.

Motivation generalizes to other things.

It’s not unique to just ingesting foods,

but foods that give us a big pulse of dopamine

will make us crave more of that food.

It will make us crave more of the activity

that led to the ingestion of that food.

And as I mentioned earlier,

a lot of that is happening at a subconscious level

that you’re not even aware of.

And this is why I think the concern about hidden sugars

and over-ingestion of sugars is serious

because it’s not just that the sugars

are impacting our blood glucose in negative ways,

although often it is,

it’s not just the obesity crisis that’s happening,

it’s also the fact that it’s disrupting our dopamine systems.

Now, that doesn’t mean all sugar is bad.

Some people have a quite healthy relationship to sugar,

but I think most people are just not aware

that sugar isn’t just operating at the level of taste,

it’s operating at the level of neurochemicals

and it’s doing it subconsciously.

So I’d like to talk about some of the other pathways

between brain and body

that regulate our moods and emotions,

but also are actionable.

So the other neuromodulator that’s really interesting

in the context of the vagus is serotonin.

Serotonin, just to remind you, is a neuromodulator,

therefore it creates a bias in which neural circuits,

which neurons in the brain and body are going to be active,

and it makes it less likely

that other ones are going to be active.

I think it’s fair to say without ever having measured it

that my bulldog Costello must just,

his brain and body must be swimming in serotonin

because he’s very calm and he eats a lot,

but he generally feels pretty sated.

He’s kind of an animal that’s obsessed with comforts.

He’s a bit of a hedonist.

And serotonin, when it’s elevated,

tends to make us feel really comfortable

and kind of blissed out wherever we are.

And that contrast with dopamine and epinephrine,

which mainly put us in pursuit of things,

motivation is pursuit.

Serotonin is more about feeling really comfy where we are.

The conversation around the brain-body relationship

and mood in serotonin for many years was,

well, you eat a big meal, the gut is distended,

you’ve got all the nutrients you need,

you rest and digest, and serotonin is released.

That’s sort of true, but there’s a lot more going on

and a lot more that’s interesting

and actionable that’s going on.

First of all, some of you, but perhaps not all,

have heard that more than 90% of the serotonin

that we make is in our gut.

And indeed, we have a lot of serotonin in our gut.

We have neurons in our gut that make serotonin.

We have neurons in our brain that make serotonin.

But here’s the deal.

Most of the serotonin that impacts our mood

and our mental state is not in our gut.

Most of it is in the neurons of the brain

in an area called the raphe nucleus of the brain.

There are a few other locations too.

And those are the neurons that control

whether or not we feel satiated or not,

whether or not we feel happy and calm.

You can’t have a discussion about serotonin

without having a discussion about antidepressants

because during the late 80s and early 90s,

there was this explosion in the number of prescription drugs

that were released,

things like first one and most famous one is Prozac,

Zoloft, Paxil, a number of other ones

that are so-called SSRI,

selective serotonin reuptake inhibitors.

That’s a long acronym,

but basically those drugs work by preventing

the gobbling up of serotonin

or reuptake of serotonin into neurons

after it’s been released,

which leads to more serotonin overall,

which means to elevate serotonin.

And indeed those drugs were and can be very useful

for certain people to feel better in cases of depression

and some other clinical disorders as well.

So I really don’t want to dismiss them

as useless or dangerous for everybody.

They can be quite useful for many people.

Not everyone responds well to them,

as I’m sure you’ve all heard,

and their side effect profile

has effects like blunting affect.

It can make people feel kind of flat, kind of meh.

It can reduce appetite for food.

It can reduce appetite for sex.

It can do all sorts of things,

or it can work really well.

Sometimes it’s a dose-related issue, et cetera.

Serotonin is fascinating, however,

because how well those neurons in the raphe work

is impacted by some events within the gut.

Although you might be surprised to find out

what those events are.

So let’s go a little bit deeper into the gut.

And again, the gut includes the stomach

and then the small intestine and the large intestine.

And ask like, what is going on with serotonin in the gut?

How is it impacting serotonin in the brain?

And let’s think about this in the context

of how some of us might want to increase

or decrease our serotonin levels.

So as far as I know,

there aren’t any really good at-home blood tests

for things like serotonin and dopamine.

There are some commercial products out there,

but to me, just to me, I’m not particularly impressed.

You know, it’s not the same

as getting your hormones levels measured

or your metabolic factors measured.

That can be done and can be done rigorously.

There are tests out there.

There are even some, believe it or not,

there’s some questionnaires, you know,

and I think actually last year

it made some of the bigger newspapers.

You know, are you more of a dopamine or a serotonin?

Are you a this or a that?

I find that stuff to be a little silly,

although I do appreciate and like the fact

that people are thinking about

and talking about neuromodulators.

There aren’t really great ways

to measure these things outside the clinic.

There’s some great clinical tools

that you can get inside of a hospital

or from a proper endocrinologist or neurologist,

but no great at-home tools.

So maybe that’s a call to arms

for some of you entrepreneurial folks out there

to create these tests, accurate tests, please,

that could be done at home.

But you know, some people feel like they’re too anxious

or they’re always in a motivated state

and they’re trying to adjust their serotonin.

Many people adjust their serotonin by just eating more food

and carbohydrate-rich foods will increase serotonin.

I’ve talked about this on a previous podcast,

but I personally am a big fan, at least for me,

as I usually fast and exercise in the early part of the day.

I eat a relatively high protein and moderate fat,

zero carb or low carb meal at lunch

and in the afternoon to stay alert

because those foods tend to favor dopamine production,

acetylcholine production,

epinephrine production, and alertness.

My mood is generally pretty good most of the time.

And then as evening comes around

and I’m concerned about sleep and a good night’s sleep,

not concerned in an anxious way,

but I want to get a good night’s sleep,

I will ingest foods that promote serotonin release

because they contain a lot of tryptophan.

So if I do eat meat,

it would be like a white meat turkey meat.

I don’t tend to, I’ve never liked turkey.

I don’t mind the animal, but I don’t like ingesting the meat.

But starchy carbohydrates will increase serotonin.

Some people also will take serotonin.

You can now buy 5-HTP supplements.

This is a little bit tricky.

5-HTP supplements can, of course, increase 5-HTP.

It is 5-HTP or serotonin,

but that sometimes can create problems

in endogenous or self-made production of serotonin.

So I’m never a fan of taking things

very close to the chemical you’re trying to increase

for very long periods of time, maybe for occasional use.

I have the problem that if I take serotonin supplements,

5-HTP, I fall asleep.

The sleep I have is very intense

and I wake up three or four hours later.

And we know based on sleep studies

with good measurements in the lab

that serotonin release tends to be

in the later part of the night.

And so by taking it early in the night,

it really can disrupt the pattern of sleep

and the depth of sleep.

Nonetheless, some people are interested in taking serotonin

to get some of the more blissed out effects.

You can achieve that with foods, as I mentioned,

that are carbohydrate rich.

So as you’re seeing,

this isn’t really a discussion about nutrition per se.

This is a discussion about food, which contains amino acids,

amino acids being the precursors to neuromodulators

and neuromodulators having a profound effect

on your overall state of alertness or calmness,

happiness, sadness, and wellbeing.

So there are a number of things that one can take,

as I mentioned, one of them being 5-HTP itself.

Now, I’m not recommending people take anything,

but if you’re interested in what this does

and you want to explore this,

of course, you’d want permission from your doctor.

You can go to this free website.

I love this resource.

They don’t pay me to say that, but I just love this resource.

I followed it for a long time, called

Thank you folks at

for putting this free resource out on the web

that has links through what they call

the human effect matrix.

So it’s links to all the PubMed studies

for particular effects of particular compounds

that one can buy and ingest.

Incredible, as well as important health warnings.

So I’m not going to read through everything,

but if you were to go to, as I have now,

and you’d put in 5-HTP,

they’re only looking at things that have strong evidence.

PubMed articles, articles are in the PubMed archive.

So for instance, I didn’t know this,

but 5-HTP produces a notable decrease in appetite.

Three studies.

And this appetite suppression makes sense, of course,

because we ingest foods to get serotonin.

And if we have enough serotonin,

then there’s no reason to ingest more foods.

It tends to have a blunting of appetite.

It probably does that also through other mechanisms.

So I’m not saying you should do this,

but if someone’s trying to blunt their appetite,

could be a interesting route.

Although I don’t recommend chronic use.

Not surprisingly, there’s a decrease in body weight

as a consequence, an increase in cortisol.

So that’s kind of important to note

that when you typically in biology,

if you pull on one string really hard, another one moves.

It’s a little bit like a puppet

and there’s more than one string on the puppet.

So it does seem to increase cortisol,

though they report as a minor effect.

Again, links to all those studies are there,

which is why I’m not listing them out in our caption notes.

You can go and get them at,

put in serotonin and you’ll find that.

So I find it fascinating that nowadays there are things

that are somewhere between doing nothing,

getting serotonin from tryptophan in foods

and prescription drugs.

There’s this other category of supplements

that are really interesting

for modulating these chemicals in the body.

And I should mention before I move on,

because I mentioned L-tyrosine,

I neglected to mention earlier

in our discussion about dopamine.

If you’re interested in the dopamine pathway,

go to, put in mucuna prurens.

It’s M-U-C-U-N-A, separate word, P-R-U-R-I-E-N-S.

It is a velvet bean that grows from vines

and is very itchy to touch due to serotonin on its surface.

Amazing, this bean has serotonin on its surface.

And indeed serotonin, if you were to put it on your skin,

would cause some irritation of the skin, amazing.

Inside the bean is L-DOPA.

Mucuna prurens is not just something

that promotes dopamine release

because of some weird mystical ancient thing

or whatever, or sorcery.

It is chemically L-DOPA, the precursor to dopamine.

It contains some other molecules as well

and low levels of other psychoactives.

This stuff is available over the counter.

Incredible, I personally find it incredible.

Its effects are really interesting.

I’m not going to read them all off,

but I mentioned these effects

not because I’m encouraging you to take it,

but because you get a window into what dopamine,

acute dopamine increase does

in the non-Parkinsonian context.

And you can start to think about foods

that are rich in L-tyrosine

as biasing certain effects or not others.

So when you hear food is medicine,

food isn’t really medicine, food is food,

but food has these chemical effects as well.

So first one listed is three studies

with a very high rigor

that overall have a minor effect on,

of all things, sperm quality.

So it appears that sperm motility itself,

I’m assuming when they say sperm quality,

I don’t know what features of sperm of quality

they looked at with sperm.

That’s not a discussion I want to have,

but I’m assuming it’s motility

because I know enough about reproductive biology

to know that sperm’s ability to swim

depends on some proteins that are present

in the front of the sperm, et cetera,

things like pentraxins,

and sperm motility is generally associated

with sperm quality.

Sperm that don’t move are generally not very useful sperm.

Symptoms of Parkinson disease

are notably degraded with macune appearance.

So fascinating, that’s not surprising.

And there are a lot of other effects here.

Feelings of subjective wellbeing,

testosterone, reductions in prolactin, not surprising.

Prolactin is a hormone that’s involved in milk letdown.

In lactating mothers, it’s involved in feelings of peace

and generally is antagonistic to sexual desire

in both men and female.

So it’s really interesting that things like macune appearance

which are L-DOPA, reduced prolactin, increased sperm motility,

increased testosterone, subjective wellbeing.

So you’re starting to see a theme, right?

Dopamine really makes us motivated,

feel in pursuit, makes us feel good.

Serotonin makes us feel more relaxed and calm.

Now, this whole month is about emotion.

So you might be thinking, well, wait,

where are we going with all this as it relates to emotions?

But in the last episode,

I said something I’m going to repeat it now briefly,

which is that much of what we talk about

is good emotions or bad emotions.

There’s a context to that.

There’s a social context.

You can’t really say an emotion is good or bad.

Grieving at a funeral is healthy, okay?

Being happy at a funeral,

assuming you loved the person that died,

is most people probably wouldn’t think that was healthy.

So we can’t really say that certain emotions

like sadness or happiness are healthy.

It’s context is important.

Cultural context is important.

Many of you have asked for book recommendations.

This is an opportunity to raise a mention of another book.

Again, I don’t have any financial affiliation or anything,

but if you want to read more about emotions

and how the context and cultural things

impact our emotions, I’m a huge fan of Lisa Feldman Barrett.

I learned about her from the Lex Fridman podcast.

I’ve had discussions with her on my Instagram Live.

She’s at Northeastern University,

a world expert in emotions.

Her first book is, How Emotions Are Made.

This is not a book she sent me.

I paid for this with my own money years ago.

Bought it, read it, loved it long before I met Lisa.

I’m just delighted that we’ve got to known each other

a little bit.

It’s a really interesting read into the psychology

of emotions and some of the subjectivity of emotions.

So whereas I’m talking about mainly the biology of emotions,

this gets a little bit more into the psychology,

although the biology as well.

And Lisa’s just terrific.

She’s also putting a lot of information out into the world

about emotions.

So if you want to learn more about that,

check out her work.

Again, it’s Lisa Feldman Barrett,

and that book is How Emotions Are Made.

Hopefully she’ll continue to write many more books.

So now you understand the relationship, I hope,

between foods and dopamine, foods and serotonin,

and that they’re both being communicated to the brain

via the vagus, right?

We ingest these foods.

These supplements are things people take.

They don’t put them directly into the brain.

They put them in our gut.

So yes, there’s a gut-brain connection,

but it’s not about the serotonin in the gut

that makes you feel calm and placid.

It’s not about the dopamine in the gut.

It’s just been oversold that way

because I think there’s something really attractive,

and I understand about the idea that

because certain things about our experience of life

and our emotions is happening in our body

that maybe we have a little more control, right?

Because this thing is a hard container.

We can’t just stuff some dopamine in there.

I can’t just, you know,

I could probably take a mucuna prurines bean

and stuff it in my ear.

Please don’t do that.

It’d make my ear itchy

because of the serotonin on the outside,

but you can’t get stuff in there.

What you have to do is ingest things

that are metabolized in certain ways

that communicate to the brain,

or so maybe they pass into the brain themselves

across what’s called the blood-brain barrier.

I’m going to talk about the blood-brain barrier in a minute.

It’s actually called the BBB.

So it ends up sounding like baby, BBB.

I guess that’s like BB.

Anyway, BBB.

But there are also nerves in the gut

that are sensing the nutrient contents of food

and then saying, oh, you should feel better and want more.

Oh, that’s got a lot of bitterness and acid taste to it.

You should want less of that, okay?

So as I transition out of the discussion

about dopamine and serotonin in the gut,

hopefully you’ve got some actionable items

there under your belt, pun intended,

where you can understand how certain foods

and certain nutrients, and you can look these up,

might impact your mood.

If you’re somebody who’s really anxious and really wired,

well, then the dopamine-adrenaline pathway,

epinephrine pathway is probably not one

that you want to lean on any harder.

If you tend to be someone who’s pretty passive

and you’re having trouble with motivation,

well, then think about ramping up the dopamine pathway.

I always think behaviors and proper food choices

is the best way to start,

and behaviors include things like exercise, et cetera.

But one of the problems with the discussion

around mood and exercise or mood and meditation

is that it’s so subjective.

It’s like, I love certain forms of exercise and not others.

Certain ones are aversive to me.

Certain ones are attractive to me.

And it’s never really clear.

No one’s ever told me, okay, you have to do 10 minutes

on the bike at X number of RPM at so-and-so

or on the skier in order to get your dopamine up.

But we can actually say, if you ingest more L-tyrosine,

there’s a high probability

that you’re going to make more dopamine.

And I’m talking about ingesting it through food

or through supplementation, if you like.

Macuna purines, I’ve tried, I should just mention.

It was too dopaminergic for me.

I really, really jazzed up

and then severe crash for me the next day.

But that’s, I think, because I tend to ride pretty high

on the kind of alertness and motivation scale.

I’m always being told by Costello

and other people in the podcast studio

to slow my speech down.

This is me uncaffeinated.

And I could probably afford a little more serotonin

in my life.

So, whereas Costello, he could afford,

well, he could afford to wake up every couple days

and just say hello to us.

This dog sleeps more than any other creature.

It’s remarkable.

So there are things that we can do and they’re actionable.

And they are, in some ways, they’re quantitative

because you can regulate dosages

and you can regulate amounts and you can regulate timing.

And everyone has to play with these things

and figure out what’s right for them in terms of feeding.

And everyone has to explore and understand

what’s safe and right for them.

But, and of course, exercise is still very important.

I talked about social connection in the last episode,

super important for activation of serotonin.

But when it comes to this gut-brain, body-brain relationship,

what we eat really matters

in terms of the neurochemicals that we make.

So let’s talk a little bit more

about things that we ingest in our body

and then allow our body to inform our brain

to shift our mood.

And this is something I’ve been doing for years.

And I just want to say,

I’ve found to be a complete game changer.

There’s excellent science to support it.

And I think most people are familiar with it

in a different context,

but I don’t think most people know this simple fact,

which is that the omega-3 to omega-6 fatty acid ratio

has a profound effect on depression.

It has a profound effect on mood.

So much so that in a double-blind placebo-controlled study

that I will provide the link to,

this was a study first published in 2008,

but there’ve been many others as well.

First of all, in an experiment done in animals,

they found there’s a model of learned helplessness

in animals.

It’s not very kind to the animals,

but they put rats or mice in a jar,

they let them swim and they’ll swim, swim, swim

to try and save their life.

And eventually they give up.

It’s a learned helplessness.

They don’t let them drown, they take them out.

Adjusting the omega-3, omega-6 ratio

so that the omega-3s are higher

led to less learned helplessness,

meaning these animals would swim longer.

Okay, now that’s an animal, that’s a rat,

not a particularly kind study.

But that same study was essentially done in humans,

although they didn’t have them swim

to the point of near drowning.

What they did is they took people

who were clinically depressed, major depression.

Okay, major depression is severe maladaptive state,

meaning it inhibits job, relationships, appetite,

all sorts of negative health effects.

And they did a comparison of 1,000 milligrams a day of EPA.

So EPA is one of the elements

that contains high levels of omega-3s

that’s in things like fish oil.

I’ll talk about other sources in a little bit,

but it wasn’t 1,000 milligrams of fish oil,

it was 1,000 milligrams of EPA.

Compared that to 20 milligrams of fluoxetine,

which is Prozac, okay, really increases serotonin.

And in this study of 60 individuals,

again, I’ll provide the links to the study,

they found that they were equally effective

in reducing depressive symptoms.

So imagine that, a food-based compound

that you can’t make without, right?

This is not a situation

where you can make your own omega-3s,

you have to get them from food sources

or from supplementation,

was as effective as 20 milligrams of fluoxetine

over the course of eight weeks.

And what was really interesting in addition to that

is that the combination of 1,000 milligrams of EPA

and fluoxetine had a synergistic effect

in lowering depressive symptoms.

I find this remarkable.

I heard about this when it first came out

and I wasn’t sure what to make of it

because there are a lot of studies that come out

and I generally like to focus my changes in behavior

around things where there’s a large center of mass,

there’s a lot of information.

A couple of years later,

I did in fact start taking 1,000 milligrams per day of EPA

in fish oil.

Now, there are a few side effects of fish oil.

People who have blood, who are bleeders,

who have factor V Leiden mutations,

or women who are taking birth control,

which can affect blood clotting and things of that sort,

really should talk to your doctor,

make sure it’s okay for you.

Fish oil also can give people fishy breath,

which is pretty gross, frankly,

but there are now fish oils

that either because of the encapsulations

or because they put some lemon flavoring in there

doesn’t have that effect.

In any event, 1,000 milligrams per day of EPA,

I started ingesting that regularly.

I just felt better.

I wasn’t clinically depressed,

but I did feel, at least for me,

an increase in mood and affect

and a number of other things

that’s supposed to reduce inflammation.

The cardiovascular effects are controversial.

For a long time, everyone thought

the effects on platelets were really terrific.

Then there were articles that came out in major newspapers

saying maybe not so much,

but the effects on mood are really profound.

And now there are lots of studies.

If you go into PubMed and you were to put EPA

or fish oil and depression,

you would find that there were a number

of really impressive results

showing that it’s at least as effective

as certain SSRIs, antidepressants, at these dosages.

And it can amplify or improve the effect of low dosages

of some of these SSRIs.

So I feel like more people should know about this.

This is nutrition, but it’s profoundly affecting mood.

And depression is terrible, right?

Depression can have a component of anxiety in some cases

where people feel lousy and very uncertain.

That’s kind of how I talk about depression with anxiety

is you talk to someone who’s anxious

and you can tell them everything’s going to be okay, okay.

And they’re always concerned

about what they might not know.

You don’t really know the plane isn’t going to crash.

You don’t really know that life is going to go okay.

And in some sense, they’re right.

No one has a crystal ball or can predict the future,

but they tend to perseverate or fixate on the uncertainty.

And then of course there are the versions of depression

that involve certainty.

People are lethargic and they’re certain.

They say, yeah, I’m certain

I’m never going to get another job.

I’m certain I’m never going to meet anyone new.

I’m certain I’m going to fail.

So there’s this kind of a divide in the sphere of depression

around certainty and uncertainty.

But what’s interesting is this thousand milligrams per day

or more of EPA has been shown to relief

both forms of depression.

Now, does that mean it’s going to work for everybody?

No, I’m not here to try and play psychiatrist.

I want to point you in the direction of these manuscripts

so that you can make informed choices for yourself.

You can discuss it with your doctor and family

and make the choices that are right for you.

But here’s what’s especially interesting

about the heart effects,

because we’ve heard that these omega-3s,

which of course you can get from other sources too.

You can get from fatty fish.

There are flax seeds, hemp seeds.

There are a number of chia seeds, these kinds of things.

But the levels of EPA that are required are quite high.

So this thousand milligrams per day,

that’s pretty hard to get from food,

although it can be done depending on what you’re eating.

What’s interesting is that the heart effects

that are solid, that really stand up in the literature,

have a lot more to do with something we talked about

in a previous episode and I’ll mention again,

which is heart rate variability.

So we know that having a heart rate that’s really high

or a heart rate that’s really low,

neither of those are good.

A lot of people think,

oh, you just want a low heart rate, big stroke volume.

You know, if you’re running a lot,

you may have 30 or 40 beats per minute.

That’s great to be in shape,

but you still want heart rate variability.

It has a lot to do with the tone

of the autonomic nervous system.

I talked about last time how when you inhale,

it speeds up heart rate.

When you exhale, it decreases heart rate.

That’s called respiratory sinus arrhythmia.

It’s the basis of heart rate variability.

We’ll maybe do a short post about this

so you can get all the mechanism

and the behaviors that spill out of that

that might be useful for you.

But the point is heart rate variability, HRV is good.

And what’s interesting is that there was a study in 2009

that showed that people who eat a diet

and fail to supplement in a way

that there’s a high omega-6 to 3 ratio,

so not enough omega-3s,

not only are there markers

of inflammatory cytokines elevated,

things like IL-6 and TNF-alpha,

but they tend to be non-responders to antidepressants.

Shifting that omega-3, omega-6 ratio did a couple things.

First of all, increasing the amount of EPA,

shifted the ratio so it was higher omega-3

to omega-6 ratio, which was good,

lowered the inflammation markers,

and then allowed antidepressants to have their effect

even at low doses.

And here’s the really interesting thing.

It worked by increasing heart rate variability.

And you think, well, how in the world would this happen?

I mean, that’s a ton of effects,

but the way it works is because of the way

that these things are impacting the gut

and the autonomic nervous system.

Remember earlier I said the vagus includes connections

from the heart signaling about sensory information

about how fast the heart is beating to the brain,

not just stuff from the lungs,

but information from the heart,

and the brain then adjusts heart rate

by heart rate variability.

So it’s incredible that there’s a way

that one can use the gut,

the ingestion of more of these EPAs,

either through food or supplementation,

to increase heart rate variability,

and thereby to improve symptoms,

meaning reduce symptoms of depression,

and to even make low levels of antidepressants

that wouldn’t otherwise work, work.

And I think I like this study so much

because A, it’s super cool.

It bridges the brain-body axis.

It incorporates nutrition and micronutrients in the brain,

but also because it really points to something

that we hear all the time,

which is that our body is a whole system.

It’s working as a whole system,

and the brain isn’t working in isolation up there

in the skull.

It’s reacting to things that are happening in the body,

in the gut, and in the heart rate,

and heart rate variability,

and that the things we ingest

can have a profound effect on them.

Now, of course, I really want to emphasize something,

which is that no one compound,

or nutrient, or supplement, or drug,

or behavior for that matter,

is going to be the be-all, end-all

of shifting out of depression,

or improving one’s mood, or improving sleep.

It’s a constellation of things.

And this is especially true

when people start to get excited

about supplements and drugs of all kinds,

and their potential for various things.

Right now, there’s a lot of excitement about psychedelics

and their therapeutic uses, and I think, great.

But as a good friend of mine,

who’s a physician clinician says,

better living through chemistry

still requires better living.

You cannot expect to take a compound,

regardless of source or potency,

and have it completely shift your experience of life

without having to continue to engage

in the proper behaviors, all the things we know,

proper sleep, exercise, social connection, food, et cetera.

There are many others as well.

So I still find that this collection of studies

about omega-3 to omega-6 ratios to be profoundly important,

so much so that it’s completely changed

the way that I think about food, the foods I eat.

I do supplement.

I don’t necessarily think that’s for everybody,

but I really think it’s incredible

that there are these compounds

that have these robust effects on our feelings of wellbeing.

And there are others too.

So that 1,000 milligram per day threshold of fish oil

that’s beneficial requires that one take

a reasonable amount of these things,

either through food or through supplementation.

I acknowledge that not everyone wants to take fish oil.

There are a couple of reasons

why one might want to avoid that.

One would be for ethical reasons.

You have an emotional relationship

or a relationship to the environment

that makes you not want to ingest fish-related products.

There’s krill oil.

Krill is still an organism.

It’s a little tiny thing that whales eat a lot of,

and people generally eat very little of.

So krill is out there.

I personally, just me, I don’t know why,

I didn’t react well to krill.

It didn’t make me feel very good.

I had some like kind of skin itchies and things like that,

and they stopped when I stopped taking it.

But I don’t want to bias you against it

if that’s your preference.

Some people really like krill oil as a source of omega-3s.

I did mention some of the other sources

like chia seeds and flax seeds.

But as you’ll notice, these are not things

that we tend to ingest a lot of on a regular basis.

It is possible to get omega-3s from meats

if the animals have grazed on grasses

that contain a lot of omega-3s.

So for those of you that ingest meat,

the source of those meats is going to be very important

as it relates to omega-3s.

Even within the category of fish oil,

there’s a concern sometimes about mercury

and other contaminants.

You want to go with a brand that emphasizes

that they’ve gone to really good sources

and that they decontaminate regardless.

And so you have to search out those brands.

There is a test that you can do

as to whether or not the fish oil is rancid or not.

Some people take in liquid form.

Some people take in capsule form.

The liquid form is going to be more affordable.

The capsule form is a little easier and a little more


You can actually just chew one of the gel tablets.

And if it tastes really fishy and kind of rancid,

you’ll know it’s disgusting.

You’ll want to spit it out.

And if it doesn’t and it’s tolerable,

then you’ll know that it’s okay.

Unfortunately, you have to buy it first in order to do that.

Although, I don’t know,

maybe you can get them to open up the bottle for you

in the store and tell them that you don’t want to try it.

Someday, perhaps fish oil and omega-3s,

it’ll be like tasting wine in a restaurant

where you can send it back.

For now, I think you have to purchase it first,

but find a brand you trust and like,

and then work with them

if you decide to go that route, of course.

There are other compounds that are also interesting

for mood elevation that are essentially like foods

or are supplement-based that now, fortunately,

there are really good data from peer-reviewed studies.

And the next one I want to mention,

because I think it’s really interesting, is L-carnitine.

Now, L-carnitine has been around a long time

and it’s been discussed in the context of heart health

and a number of other things.

It was actually in tout as a bit of a weight loss agent

in the early 90s.

But L-carnitine actually has some really impressive effects

on depression.

And again, we will look to PubMed

because looking at is essentially,

for me anyway, looking at PubMed, what is L-carnitine?

Okay, L-carnitine is most prevalent in meat

and in beef in particular.

Now, for the vegans, please know that L-carnitine

is available through non-meat sources as well,

although it’s not as enriched in non-meat sources.

It’s a really interesting molecule

because L-cetyl L-carnitine

is essentially what’s made from L-carnitine,

but it’s acetylated.

If you’re interested in the biochemistry,

you can look that up.

It’s acetylated into a form

that can cross the blood-brain barrier.

The blood-brain barrier or BBB is a barrier.

It’s a wall around the brain.

And you have this barrier because the brain is so important

and it has this feature that the neurons there

don’t recreate themselves after injury

like other organs of the body.

There’s not a lot of turnover of cells

despite what you might’ve heard.

And so nature has created this BBB,

this blood-brain barrier,

to make sure that certain molecules,

in particular large molecules,

don’t get across the blood-brain barrier

because it can be damaging to those tissues.

Incidentally, you also have a very rigid

or stringent barrier around other organs,

which are the gonads.

So the ovaries and the testes and the brain

are the organs of the body

that nature has gone out of its way to protect,

give this additional layer of the blood-brain barrier,

or as you might imagine for the testes and the ovaries,

it’s going to be the blood-gonadal barrier.

So these barriers exist and make it such

that just because you eat something,

just because you ingest it,

doesn’t mean it’s going to cross the blood-brain barrier.

But L-carnitine, when taken,

is acetylated and converted into this form

that gets across the blood-brain barrier.

And it has a lot of effects.

It’s involved in mitochondrial activation

of long-chain fatty acids, which that’s a big mouthful

that we could get into sometime

when we’re talking about metabolics,

but it has some interesting effects on the neuro side.

So if you decide to check it out on,

you’ll see some really interesting things,

lots of effects on ammonia, C-reactive proteins,

things of that sort, blood glucose is lowered, et cetera.

That’s all stuff that’s the level of blood in periphery,

slight effects in lowering cholesterol.

Here’s some interesting ones.

Rates of pregnancy go way up

when people are taking L-carnitine.

Both the father and the mother,

both the source of sperm and the source of egg

are affected in ways that favor pregnancy.

It does increase, here we go again,

with sperm quality, sperm motility in males.

And it seems to have positive effects on females

that have polycystic ovary syndrome.

So check that out.

The effects are very strong.

There are three studies listed there.

Again, I’m not promoting this,

but that people take L-carnitine,

especially if you’re trying to get pregnant,

but check it out because the effects there

and the studies that are mentioned

are published in peer-reviewed rigorous journals.

In terms of the neural effects, those are quite interesting.

The effects on depression are still emerging,

but they do seem to exist,

that people feel a notable decrease in depressive symptoms.

There are seven studies listed on

that it has a notable benefit in a variety of circumstances

where participants have heightened depression already.

They start taking L-carnitine and they start feeling better.

And they talk about dosages in those various studies.

It also has been shown to have a notable decrease

in the symptoms of autism, which I find fascinating.

Also, again, the things we ingest

impact the chemicals in our brain

and how they impact the rest of our body.

There’s other things that’s been used

to treat certain forms of alcohol dependence.

I think this is going to be a very exciting emerging area.

We’re going to do a whole month about addiction.

I’ve got a great guest lined up for that month,

but there’s now an emerging field

about what people can take and supplement

to help ease the cravings and the withdrawal

when trying to quit drugs of abuse like cocaine,

alcohol, heroin, and smoking and things of that sort.

So really interesting area.

This is, I like to think is early days

and we’re going to discover a lot more.

There’s a huge list of things here.

Since we talked about pain on a previous episode

and I know a lot of people have written to me

about fibromyalgia, L-carnitine has been shown

to reduce symptoms of fibromyalgia.

Again, all the links to studies are on,

totally free site.

And that was my bulldog being a battering ram.

There’s nothing graceful about this bulldog.

He’s decided he wanted to leave to go get a drink of water.

And so please forgive the noise.

Okay, so now let’s turn to another aspect

of the gut brain relationship that will surprise you,

in some cases might shock you,

and that has some really cool and actionable biology.

And that’s the gut microbiome, probiotics, and prebiotics.

I know today we’re talking about emotions and not pain,

but I’d be remiss if I didn’t mention another effect

of acetyl L-carnitine that’s been reported

and that you can find listed with link to study

on, which is its effect

in reducing the symptoms of migraine.

This was a randomized control trial

with 133 participants who had frequent migraines.

They were taking 500 milligrams of L-carnitine

or nothing for 12 weeks.

So the control is a little bit,

the control experiment there is a little bit tricky,

but it had a significant effect

on reducing the number of migraine attacks per month.

So I find that really interesting.

And there’s a lot more listed there about the study.

And I think these compounds are powerful.

They carry risks for certain people, not for others.

So again, you have to find out what’s right for you,

but I do think they are super interesting

as potential therapeutics for various people.

So what’s the deal with the gut microbiome

and the gut-brain axis?

Today, we’ve actually been talking a lot already

about the gut-brain axis

that has nothing to do with microbiomes.

We’ve been talking about this vagus nerve

that connects providing sensory information

from the body to the brain.

And then the brain also sends in the same nerve

motor information to control the motility,

the gut, the heart rate, how fast we breathe

and deployment of immune stuff,

killer cells and things of that sort.

But oftentimes when we hear

about the gut-brain axis these days,

it’s a discussion about the gut microbiome.

And once again, we’re in a situation

where there’s incredible biology.

I’m very happy there’s so much discussion

about the gut microbiome.

I am somewhat dismayed and concerned

that most of what I hear out there

is either false or partially false.

So we’re going to clear up some of the misconceptions

first by understanding the biology.

And then we’re going to talk about

some of the actionable items.

It is true that we have a lot

of these little microorganisms living in our gut.

They’re not there because they want to help us.

They don’t have brains.

They are adaptive, however,

they try and find and create environments

that make it easier for them to proliferate.

So they don’t care about you and me,

but they are perfectly willing to exploit you and me

in order to make more of themselves.

The same way viruses are.

Viruses don’t have a mind, they infect cells,

they hijack the genome

and they use that genome to make more of themselves.

The microbiota that live in us

vary along the length of our digestive tract.

But let’s just take a step back

and think about how our body plan is made.

We are actually a series of tubes.

Our brain is actually a tube.

You see, it’s all squishy on the outside.

And then it’s got that long thing,

the spinal cord that goes down to the base of the spine.

That’s the central nervous system.

That all started out as a tube.

It just looks like a cauliflower on the other end

up in the brain because the tube is so big

and it has to be crammed into the skull

so it gets all wrinkled up.

But if we were to splay it out,

you’d find that it’s just one big tube.

Similarly, our digestive tract and our airways

are essentially one big tube.

It starts with our mouth, also our nose.

And then we have all these other tubes

that go down through our throat and then into our stomach

and then into our various intestines.

And then the tube ends out the other end.

So we are one long tube for digestion.

And inside of that tube is a mucosal lining.

It’s these little microvilli, tiny, tiny, tiny,

little like velvety ends of cells

that are able to move and move things along.

And mucus, mucosa.

And the conditions of that mucosal lining

set a number of different things.

It sets the rate of our digestion

and the quality of our digestion.

It sets, for instance, our immune system.

Most people probably don’t realize this,

but most infections in the environment,

well, they have to get into our body somehow.

Some of them are inhaled.

A lot of them go into our mouth

and lodge in the mucosal lining of the mouth.

And then infections start there.

You probably had the experience, unfortunately,

of feeling like you have a tick in your throat,

like something’s irritating your throat.

And then it kind of migrates up into a head cold

or runny nose.

Sometimes it’ll start as a headache.

Sometimes it won’t.

But things that can migrate down into the gut.

So we’re ingesting things all the time.

Think about air, bacteria, viruses,

they’re making their way into our gut.

And some of those bacteria live in the gut.

And some of those bacteria

bias the mucosal lining in the gut,

stomach and intestines,

to be more acidic or more basic

so that they can make more of themselves,

so they can replicate.

They like a particular comfort.

It’s like they like a particular kind of bedding

to lie down in and create more of themselves.

Now, some of those mucosal linings that they promote

make us feel better.

They make us feel more alert.

They bolster our immune system

and others make us feel worse.

So first rule,

the microbiome isn’t good or bad.

Some of these little bugs that live in us

do bad things to us.

They make us feel worse.

They lower our immunity.

They affect us in negative ways.

Some of them make us feel better.

And they do that mainly by changing the conditions

of our gut environment.

In addition to that,

they do impact the neurotransmitters

and the neurons that live in the gut

and that signal up to the brain

to impact things like dopamine and serotonin

that we’ve been talking about previously.

So there’s a vast world now

devoted to trying to understand what sources of food,

what kinds of foods are good or not good

for the gut microbiome.

So let’s just talk about some general rules of thumb

related to the research,

quality research that’s peer reviewed.

And then in a future episode,

we will go far deeper into the gut microbiome

and gut brain axis.

But here’s a few things

that I think you might find surprising.

First of all,

supporting a healthy gut microbiome is good for mood,

great for digestion and great for immune system function.

However, that does not mean maxing out

or taking the most probiotic and prebiotic

that you can possibly manage.

As I mentioned many times before,

I do believe in probiotics, I take probiotics,

but there are studies that show

that if you take lots and lots of certain probiotics

like lactobacillus and you really ramp up the levels more,

it is not a case of more is better.

There are things like brain fog that can come from that.

Brain fog is just this inability to focus.

People feel really not well generally.

Some of those studies are a little bit controversial,

but I think it’s fair to say

that if people really increase the amount of probiotic

that they’re taking beyond a certain amount,

then they start feeling foggy in the mind.

Now, what’s too much?

Well, I get probiotics from,

I’ve mentioned before, from athletic greens.

You can get them from fermented foods like sauerkraut,

pickles, kimchi, natto.

These are different sources from around the world.

Actually, I’d love to hear some of the other sources

that people know, other foods from around the world.

I’m fascinated by the way in which different cultures

have all arrived at these foods that provide

and support healthy microbiomes because they’re fermented.

I have a colleague at Stanford, Justin Sonnenberg.

He and I have talked about this.

I don’t want to quote him inappropriately,

but we’ve had discussions about it

and they’ve published that the ingestion of fermented foods

is one of the best ways to support healthy levels

of gut microbiota without exceeding the threshold

that would cause things like brain fog.

So foods and fermented foods are going to be the best source

and there are a number of different ways

that one could do that.

Some people don’t like fermented foods, however.

Some people supplement it.

So it isn’t a case of more is better.

Okay, so we know that.

The other is that it is true that healthy gut microbiota

have been shown to improve symptoms

of certain psychiatric illnesses,

as well as certain conditions like particular features

along the autism spectrum, which is interesting.

And those effects are probably due

to not just improvement of immune system function,

but to the conditions in which the neurons

that sense nutrients convey information to the brain

and increased levels of serotonin and or dopamine.

So gut microbiome provides kind of a foundation

for healthy gut and healthy gut brain access.

So much so that some people report

that when they start eating small bits,

because it doesn’t require a lot of fermented foods,

that their overall mood is better.

Not unlike the effects of EPA,

although I don’t think it’s been looked at directly

in the context of clinical depression yet.

And if someone knows of a study,

please mention it in the comments.

That would be terrific.

There are some things that you can do

to really damage your gut microbiome.

And this is where there’s a huge misconception

that I want to clear up.

There was a study that was published in Nature,

which is among the three top journals

that we have in science.

You know, Nature, Science, and Cell

are considered the top tops,

but excellent journal that showed

that artificial sweeteners,

but a particular artificial sweetener, which was saccharin,

can disrupt the gut microbiome

in ways that is detrimental

to a number of different health markers,

increasing inflammatory cytokines

and all the other bad things that happen

when the gut microbiome is thrown off kilter.

That study was widely discussed,

but there were a few things that were not mentioned there

that are really important.

That study was about saccharin in particular.

Saccharin is not the most typical

artificial sweetener that’s used.

The most typical artificial sweeteners that are used

are things like aspartame, so-called NutraSweet,

or sucralose, or these days stevia.

There’s monk fruits.

To my knowledge, and please correct me

if anyone knows of any studies.

To my knowledge, the negative effects

of these artificial sweeteners on the gut microbiome

were restricted to saccharin.

Now, there is enough chemical similarity between saccharin

and some of the other ones that I mentioned,

but not all of them.

For instance, stevia, monk fruit,

are distinct in their chemical makeup

so that they probably don’t have,

if they have any, have lower effects,

negative effects on the gut microbiome,

but it should still be tested.

So saccharin is really,

it was shown in this study and several other studies,

can really negatively impact, excuse me,

the quality of the gut microbiome.

Interestingly, the narrative around artificial sweeteners

and gut microbiome is incorrect.

Most people thought, oh, saccharin is bad for the microbiome.

It must kill the microbiome.

And so you hear people saying, oh, you know,

artificial sweeteners kill the microbiome.

That’s not true at all.

In fact, in that very same study published in Nature,

they showed that the negative effects of saccharin

on the microbiome could be blocked or eliminated

by giving antibiotics.

So what happens is certain artificial sweeteners,

in particular saccharin, disrupt the microbiome

and make the environment within the gut,

that mucosal lining, more favorable to bacteria microbiota

that are not good for the organism, okay?

This is an important distinction.

It’s not just that a language thing where people say,

oh, you know, it kills the microbiome.

It doesn’t kill the microbiome.

It shifts the microbiome.

And shifts in the microbiome can be good

or they can be bad.

And that takes us to another topic.

That’s a bit of a hot button topic,

but I’m willing to go there

because I think it deserves conversation,

which is nowadays there are many examples out there

where people have switched from a kind of standard diet

or even a vegetarian diet or vegan diet to a keto diet.

Now, keto doesn’t necessarily have to mean

the ingestion of meats, but it can.

And they experience positive effects for themselves.

Not everybody, and I’ve talked previously

about some of the kind of the incorrect,

what I believe is incorrect marketing of keto

as it relates to the cosmetic effects

and some of the challenges with sleep that some people have.

But some people love keto and it works great for them.

But the ketogenic diet is interesting

because when one shifts to the ketogenic diet,

there is a shift in the gut microbiome

and some people end up feeling better.

Some people end up feeling worse.

Likewise, some people go from ingesting animal products,

including meat or they’re vegetarian and they go to vegan,

and they experience positive shifts in mood and affect.

And we know that the transition to a more plant-based diet

and especially the enrichment of fiber

that’s present in those diets

also creates dramatic shifts in the gut microbiome.

Some people feel better doing that.

Some people feel worse.

And of course, it’s going to depend on whether or not

you’re ingesting a lot of processed foods or not.

There was a paper published in Cell,

a Cell Press Journal, obviously, excellent journal,

showing that ingestion of processed foods,

regardless of whether or not they come from animal sources

or non-animal sources,

the processed foods themselves tend to create activity

within the body.

And this surely has roots in the nervous system

that lead to overconsumption of calories and weight gain,

even some weight gain that couldn’t be explained

by increased calories.

In other words, processed foods are bad

regardless of whether or not you’re talking

about animal products or non-animal products.

Probably not surprising now,

given what you know about these sugar-sensing

and other amino acid-sensing cells in the gut

that we talked about earlier.

So the point of all this is that when I say

you have to find what’s right for you,

that’s not a throwaway statement.

Some people’s microbiome and the lining of their mucosa,

excuse me, their mucosal lining of their throat,

of their gut, of their nose,

everything is improved by diets that are heavily meat-based

and don’t have many plants.

Other people do much better on a plant-based diet

without many meat products or animal products.

It’s highly individual.

And this probably has roots in genetic makeup.

This probably has roots in what people were raised on.

Because remember, the nervous system, of course,

is set up by your genes, your genetic program,

but your nervous system, it adapts early in life

to your conditions.

That’s what it’s for.

The reason you have a nervous system

is to move your body appropriately

towards things that are good for you

and away from things that are not.

But also, it was designed to adapt.

The early life period has this incredible thing

about plasticity that we spent a whole month on

so that it can change so that, yes, indeed,

some people may like certain foods

and react to certain foods better than others

because of the way that their nervous system was wired,

this enteric, as it’s called, nervous system

that lines the gut and that communicates with the brain.

So most of what I’ve talked about today

is black and white.

These are things that are present in all of us,

the sugar-sensing neurons of the gut,

the way the vagus is wired,

the fact that omega-3, omega-6 tend to improve,

the ratios tend to impact mood

with high omega-3, omega-6 ratios improving mood.

We talked about all sorts of things

in the gut-brain and body-brain axis.

But when it comes to the microbiome,

the key thing is that we all have a microbiome.

You want a microbiome,

but you want to promote the microbiome

that is right for you.

And that can be shifted and steered

by ingesting certain categories of foods and not others.

And one thing that really frustrates me

is when the people show up with an agenda

like all-meat agenda or a vegan agenda or a keto agenda,

and they talk about these positive effects

on the gut microbiome, and it’s all true, frankly.

And so it’s highly individual.

Now, this doesn’t get to any of the ethical issues

around animals or the planet

and you hear rabid debates about that on both sides.

And I am not qualified or equipped to talk about

whether or not regenerative agriculture

or animal products or farming or any of these things,

how those actually impact the environment.

That is not my expertise.

But when it comes to your health and your microbiome,

you want to support the microbiome.

It’s very clear that these fermented foods

support the microbiome,

that we should be ingesting at least two servings per day,

which is quite a lot.

That supplementation at low levels can be good.

Supplementation at high levels can create this brain fog,

even though some people say that result is controversial.

I’ve experienced this myself

and the data look to me pretty darn solid.

So that’s one thing to think about as well.

And the other thing about the gut microbiome

is that it’s highly contextual

based on other things that you’re doing.

So even things like exercise and social wellbeing

and connection,

those things are also impacting the gut microbiome.

So find the diet that’s right for you

and that works for you in the context of the other ethical

and lifestyle choices that are important to you.

That’s my advice.

A note about fasting.

I have a colleague at Yale

who’s an expert in the gut microbiome

and he told me something really interesting,

which is when we fast,

we actually digest certain components

within our dietary tract.

It actually depletes a good amount of the gut microbiome.

And this is interesting.

I’ve had good results from,

I guess you would call it intermittent

or kind of circadian type fasting

where I’ve never done long fast,

but where I push out my first meal by a few hours.

My first meal is generally around lunchtime or so.

But the longer periods of fasting

that go for a day or two or three days

are known to deplete the gut microbiome in major ways.

But that’s not always necessarily a bad thing

because when it’s replenished,

it often is replenished at levels

that exceeded its previous level.

But I think that some of the GI tract

and even some of the mental effects

of returning to eating after feeding,

sometimes people don’t feel so good when they start eating,

they really want food, but then they start eating again,

they don’t feel as good as they did on the fast.

Some of that may be related to the depletion

of the microbiome that occurs during long fast.

So again, this is something to think about

and talk about with your doctor.

But the idea that fasting across the board is good,

there may be some merits to that,

and certainly in some cases,

but it does deplete the microbiome.

And that depletion of the microbiome is significant

because it means when you return to eating,

you’re actually not in the same position

to digest and assimilate those foods.

And those foods are not in the same position

to impact your brain and body

the same way they were prior to the fast.

And this is, I think, why people suggest

a kind of gradual transition back

to consuming nutrients after a fast.

So as we round up, I want to share some results with you

that without question will impact the way

that you respond to food mentally and even physically.

And I know that because that’s the central theme

of the studies I’m about to tell you about.

I have a colleague at Stanford, Aaliyah Crum,

who’s done some remarkable experiments on mindset.

And some people could think about these

as placebo effects or belief effects,

but they actually go way beyond those terms.

And there are a number of different examples of this

that Aaliyah’s lab and her coworkers have demonstrated,

but two that are particularly interesting to me,

I want to share with you now,

because they really emphasize how our beliefs

can really impact the way

that our brain and body work together.

I think the most famous of these is an experiment they did

where they had two groups of individuals,

they were each given a milkshake,

and they had some factors measured from their blood

by an IV while they ingested the milkshake

and then afterwards as well.

And one of the factors that they were looking at

was something called ghrelin, G-H-R-E-L-I-N.

Ghrelin is a peptide that increases with hunger.

So the longer you haven’t eaten, the ghrelin goes up.

And I know some of you say, well, I fast, I fast, I fast,

and I eventually lose my appetite.

Well, ghrelin still goes up and then it drops.

So if you were one of these people

that eats every three hours regularly,

ghrelin kind of gets a little pulse

as you get to that two hour and 50 minute mark.

So it’s a little bit of a timer as well.

It’s a really interesting peptide.

In any event, what they did is they gave people milkshakes,

two groups, one group got a shake

that they were told was a low calorie, healthy shake.

The other group got a milkshake

that they were told was the very decadent high calorie shake

I think it was something like two

or maybe even two and a half times

as many calories as the other, perhaps even more.

I don’t recall the details,

but you had a high calorie and a low calorie condition.

And then they drank the shake

and then they measured ghrelin in these subjects’ blood.

And what they found was that the high calorie shake

had a much more robust effect on blunting ghrelin

and reducing ghrelin.

But the interesting thing you probably guessed already

is that it was the exact same shake given to both groups.

So people’s belief about the content of something

impacted their physiology.

And this speaks to these so-called top-down mechanisms

or modulation of our physiology.

The previous episode about pain,

we talked about the effects of obsessive,

believe it or not, it was kind of obsessive infatuation

and love on pain responses and pain thresholds.

This is yet another example where beliefs

or subjective feelings can impact physiology

at the level of the periphery

because ghrelin is released in the periphery in the body.

Now, these belief effects extend beyond examples like this.

Another good example that I’d like to share

is Allie, Dr. Crumb, and her colleagues did an experiment

where they took housekeepers, hotel,

they were essentially hotel workers,

divide them into two groups.

They had them watch a short film.

In one case, the film was about how their work was important,

it helped people feel comfortable in the hotel,

et cetera, et cetera.

The other group heard that the activity

that they were doing, cleaning and taking care of the hotel

was good for them, it was good for their health,

et cetera, et cetera.

They controlled very nicely in the study

for health parameters, for individual differences,

and for the behaviors of these people

in the period that followed this short tutorial.

What they found was eight weeks later,

the group that had been told

that the activity was good for them

showed lower blood pressure,

they had lost a significant amount of body fat,

and they reported enjoying their work

far more than the other group.

The same work, simply biased mentally

by the information that they were given,

but their physiology followed that information.

And so this is not just the placebo effect,

this is an incredible set of findings

that illustrate the extent to which

whether or not we believe a food

is going to be good for us or not good for us,

well, we can’t escape the reality.

You can’t tell yourself that a poison

is going to be good for you and ingest that poison

and expect it to not kill you,

nor can you tell yourself that eating 12 croissants,

confess I’ve done it,

it was after a very long run, a long time ago,

but you can’t tell yourself

that that’s necessarily going to be good for you

or that it’s going to make you lose weight.

These belief effects are not about lying to yourself.

In these cases, in these experiments,

as you’ll notice,

the subjects didn’t have prior knowledge about ghrelin

or about the effects of their daily routine

on weight loss and blood pressure.

So in order for them to work,

you have to be naive to the information, right?

You can’t simply lie to yourself

and tell yourself what you want to believe.

And that’s important,

but also important is that the mind and the body

are in this fascinating interplay.

And today we’ve talked mainly about

how the body and things that we put inside this tube,

that runs from our mouth to the other end,

to our rectum basically is impacting all these cells,

these neurons, microbiota in there,

mucosal lining, heart, lungs,

and how all that information is feeding up to the brain

to impact how we feel up here.

But also how we feel up here

is impacting how our body reacts

at levels of very core physiology

that you couldn’t just tell yourself

that this was going to work.

But what you believe about certain substances,

certain foods, certain nutrients

does have a profound effect

on the magnitude of their impact.

And sometimes even the quality

and direction of that impact.

Well, first of all,

I want to thank everybody

for their support of this podcast.

The response that we’ve received

since releasing at the beginning of the new year

has been tremendous and we’re so grateful for it.

I know some of you and people you know have said,

well, it’s a lot of information.

It’s like a college lecture.

Indeed, there’s a lot of information,

but I believe very strongly that if you learn mechanism

and maybe even if you hear it several times over,

eventually those mechanisms become embedded

into the way that you view an entire topic.

As well, I always try and put tools as I go along

that you can look to immediately.

Some of them might be right for you.

Others might not.

Try them if you like and don’t if you don’t want to.

And if they don’t work for you, then discard them.

If however, you are finding benefits

from the information and from the tools

and you know others that you think could benefit from it,

please pass along information about the podcast.

Please subscribe to the YouTube channel

if you haven’t already.

Please subscribe to us on Apple and Spotify

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All those things really help us.

In addition, please check out our sponsors

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That’s one of the best ways to help support us.

And we do believe in all the products that we support

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Otherwise we wouldn’t be working with them.

And as mentioned at the beginning of today’s episode,

we are now partnered with Momentous Supplements

because they make single ingredient formulations

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and they ship international.

If you go to slash Huberman,

you will find many of the supplements

that have been discussed on various episodes

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and you will find various protocols

related to those supplements.

So today’s episode, we took a full journey

into the brain-body relationship

and discussed a lot of the mechanisms

and the actionable items that you can approach

if you want to explore this aspect of your biology

and psychology further.

Last but certainly not least,

I want to thank everybody for your time and attention today.

And as always, thank you for your interest in science.

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