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70__transcript.txt
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[upbeat music]
- Welcome to
the Huberman Lab Podcast
where we discuss science
and science-based tools
for everyday life.
I'm Andrew Huberman,
and I'm a professor of
neurobiology and ophthalmology
at Stanford School of Medicine.
Today, we are going to
discuss the gut and the brain,
and we are going to discuss how your gut
influences your brain and your
brain influences your gut.
As many of you probably know,
there is a phenomenon
called your gut feeling,
which tends to be something
that you seem to know
without really knowing how you know it.
That's one version of the gut feeling.
The other is that you sense
something in your actual gut,
in your body, and that somehow drives you
to think or feel or act
in a particular way,
maybe to move towards something
or to move away from something.
Now, today, we aren't
going to focus so much
on the psychology of gut feelings
but on the biology of gut feelings
and how the gut and brain interact.
Because indeed your gut is
communicating to your brain
both directly by way of
neurons, nerve cells,
and indirectly by changing
the chemistry of your body,
which permeates up to your brain
and impacts various
aspects of brain function.
But it works in the other direction, too.
Your brain is influencing your entire gut.
And when I say entire gut, I
don't just mean your stomach,
I mean, your entire digestive tract.
Your brain is impacting things
like how quickly your food is digesting,
the chemistry of your gut,
if you happen to be
stressed or not stressed.
Whether or not you are under
a particular social challenge
or whether or not you're
particularly happy
will in fact adjust the
chemistry of your gut
and the chemistry of your gut in turn
will change the way that your brain works.
I'll put all that together for you
in the context of what we
call the gut microbiome.
The gut microbiome are the
trillions of little bacteria
that live all the way
along your digestive tract
and that strongly impact the
way that your entire body works
at the level of metabolism,
immune system, and brain function.
And of course, we will discuss to tools,
things that you can do
in order to maintain
or improve your gut health.
Because as you'll also soon see,
gut health is immensely important
for all aspects of our wellbeing
at the level of our brain,
at the level of our body,
And there are simple, actionable
things that we can all do
in order to optimize our gut health
in ways that optimize
our overall nervous system functioning.
So we will be sure to review those today.
This episode also serves
as a bit of a primer
for our guest episode
that's coming up next week
with Dr. Justin Sonnenburg
from Stanford University.
Dr. Sonnenburg is a world
expert in the gut microbiome
and so we will dive really
deep into the gut microbiome
in all its complexity.
We'll make it all very simple for you.
We will also talk about
actionable tools in that episode.
This episode is a standalone episode,
so you'll get a lot of
information and tools,
but if you have the opportunity
to see this episode first,
I think it will serve as a nice
primer for the conversation
with Dr. Sonnenburg.
Before we begin,
I'd like to emphasize that this podcast
is separate from my teaching
and research roles at Stanford.
It is however, part of
my desire and effort
to bring zero cost to consumer information
about science and science-related tools
to the general public.
In keeping with that theme,
I'd like to thank the
sponsors of today's podcast.
Our first sponsor is Athletic Greens.
Athletic Greens is an all-in-one
vitamin mineral probiotic drink.
I've been using Athletic Greens,
which is now called AG1, since 2012
so I'm delighted that they're
sponsoring the podcast.
The reason I started
taking Athletic Greens
and the reason I still
take Athletic Greens
once or twice a day
is that it covers
all of my foundational
vitamin and mineral needs
and also because it contains
high quality probiotics and prebiotics,
which is a topic that we're
going to talk a lot about today.
With Athletic Greens, I can
be sure that I'm getting
all the vitamins and minerals that I need.
So if I'm missing anything in my diet,
I can compensate for that
with the Athletic Greens.
Plus it has the probiotics and prebiotics
that can also compensate
for any deficiencies
that I might have in creating
the right environment
for my gut microbiome.
If you'd like to try Athletic Greens,
you can go to athleticgreens.com/huberman
to claim a special offer.
They'll give you five free travel packs,
which make it very easy
to mix up Athletic Greens
while you're in the car or on a plane
or otherwise on the move,
and they'll give year's
supply of vitamin D3 K2.
While not everyone needs
additional vitamin D3,
many people do even if they're
getting sufficient sunlight.
So you get the year's
supply of vitamin D3,
and it also has K2 in there.
K2 has been shown to be important
for various aspects of calcium regulation,
cardiovascular health, and so on.
Again, go to athleticgreens.com/huberman
to claim this special offer.
Today's episode is also
brought to us by LMNT.
LMNT is an electrolyte drink
that contains no sugar.
It does however contain sodium,
magnesium, and potassium.
I've talked about sodium
on the podcast before.
I think sodium can indeed be
problematic for some people
with hypertension or pre-hypertension,
but for many people,
sodium is a great thing.
It can increase blood volume
in ways that can be helpful to them.
It can improve nerve cell function in ways
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and for me, anytime I'm
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If you'd like to try LMNT,
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You only pay the cost of shipping.
Again, that's drinklmnt.com/huberman
to claim a free sample pack.
Today's podcast is also
brought to us by InsideTracker.
InsideTracker is a
personalized nutrition platform
that analyzes data from your blood and DNA
to help you better understand your body
and help you reach your health goals.
I've long been a believer in
getting regular blood work done
for the simple reason that
many of the things that impact
your immediate and long-term
health can only be assessed
with a quality blood test.
And nowadays with the
advent of modern DNA tests,
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is and how that compares
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Now, one of the major problems
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they'll tell you if those
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With InsideTracker, they
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So these could be nutrition protocols,
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Okay, let's talk about
the gut and the brain
and how your gut and your brain
communicate in both directions.
Because as I mentioned before,
your gut is communicating all the time
with your brain and your brain
is communicating all the time
with your gut.
And so the two are in this
ongoing dance with one another,
that ordinarily is below
your conscious detection
although you're probably
familiar with the experience
of every once in a while
getting a stomach ache
or of eating something that
doesn't agree with you,
or conversely eating something
that you find particularly delicious
and that sensation or
that experience rather
being a whole body experience.
Your mind is excited about
what you're eating or just ate,
your gut is excited about what
you're eating or just ate,
and it seems to be a kind
of unified perception
of both brain and body.
Today, we're going to talk
about how that comes about
in the negative sense.
Like, you know, when you meet
someone you really dislike
or when you have a stomach ache,
and in the positive sense,
when you interact with somebody
that you really, really like
and you'd like to spend more
time with them, for instance,
or when you eat something
that you really, really like
and you'd like to spend
more time with that food,
so to speak.
Now, the gut and the brain
represent what we call
a biological circuit,
meaning they include different stations.
So station A communicates with station B,
which communicates with
station C, and so on.
And as I mentioned earlier,
it is bidirectional.
It's a two-way street
between gut and brain.
I want to make the important
point at the outset
that when I say the word gut,
when I refer to the gut,
I am not just referring to the stomach.
Most of us think that the
gut equates to the stomach
because we think of having
a gut or not having a gut
or having a gut feeling of some sort.
But in the context of gut-brain signaling
and the related microbiome,
the gut includes the
entire digestive tract.
That's right, from start to finish
the entire digestive tract
so much so that today
we're going to talk about,
for instance, the presence
of neurons, nerve cells,
that reside in your gut
that communicate to specific
locations in the brain
and cause the release of
specific neurochemicals,
such as the neurochemical
dopamine or serotonin,
that can motivate you to seek
more of a particular food
or type of interaction or behavior,
or to avoid particular foods,
interactions, and behaviors.
And some of those neurons,
many of those neurons, in fact,
reside in your intestines,
not in your stomach.
They can be in the small
intestine or the large intestine.
In fact, you actually have
taste receptors and neurons
located all along your digestive tract.
You have neurons that are located
all along your digestive tract
and they are communicating to your brain
to impact what you think, what
you feel, and what you do.
Okay, so for the gut-brain axis,
we need to deal with the brain part
and then we need to
deal with the gut part.
Let's just quickly talk
about the brain part
because there the word brain
is also a bit of a misnomer
in that when we say the gut-brain axis,
it does include the brain
but includes a lot of
other things as well.
So as many of you probably know by now,
if you're listeners of this podcast,
and if you don't, that's fine,
your nervous system includes your brain
and your spinal cord
and those together constitute
what's called the central nervous system.
Your neural retinas,
which are lining the back of your eyes
and are the light sensing
portion of your eyes
are also part of your
central nervous system.
So actually your eyes
are part of your brain.
They're the only parts of your brain
that are outside the cranial vault.
So your retinas, your brain proper,
and your spinal cord make up
the central nervous system.
The other parts of your
nervous system constitute
what's called the
peripheral nervous system,
which are the components
of your nervous system
that reside outside the
retinas, brain, and spinal cord.
Now, this is very important
because today we're going to talk a lot
about how the gut
communicates with the brain.
And it does that by way
of peripheral nervous system components,
meaning nerve cells that reside in the gut
and elsewhere in the body
that communicate to the brain
and cross into the central nervous system
to influence what you think
and what you feel, okay?
So that's the nervous
system part of what we call
the gut-brain axis,
brain, again, just being a shorthand
for including all the
elements I just described.
Gut, as you now know,
includes all the elements
of the digestive tract.
Let's talk about the
architecture or the structure
of the gut of your digestive system.
Now, not surprisingly
your digestive system,
aka your gut, begins at your
mouth and ends at your anus.
And all along its length,
there are a series of sphincters
that cut off certain chambers
of the digestive tract
from the other chambers.
Now, also along this tube that
we call the digestive tract,
there's great variation
in the degree of acidity,
or pH as it's sometimes called.
That variation in acidity
turns out to give rise
to different little microenvironments
in which particular
microbiota, microbacteria,
can thrive or fail to thrive.
And so the way I'd like you to think
about the digestive tract,
this gut component of the gut-brain axis,
is that it's not just one component.
It's not just your stomach
with a particular acidity
and a bunch of microorganisms
that work particularly well
to make you feel good
and make your digestive
pathways work well.
It's a series of chambers,
little microenvironments,
in which particular microbiota thrive
and other microbiota do not.
And certain behaviors that you undertake
and certain experiences that you have
will adjust those
microenvironments in ways
that make particular
microbiota, certain bacteria,
more likely to thrive and
others less likely to thrive.
We'll talk about how that was
set up for you early in life.
Actually from the moment
that you came into the world,
that microbiome was being established.
It was actually strongly impacted
depending on whether or not
you were born by C-section
or by vaginal birth.
And it was strongly
impacted by who handled you
when you came into the world,
literally the hands that were on you.
How much skin contact you had,
whether or not you were
a preemie baby or not,
whether or not you had pets at home,
whether or not you were
allowed to play in the dirt,
whether or not you were
allowed to eat snails
or whether or not you were kept
in a very antiseptic environment.
All of those experiences
shaped these little microenvironments
and shaped what constitutes best or worst
for those microenvironments, okay?
So you have this long tube that
we call the digestive tract
and it's very, very long.
In fact, if we were to splay it out,
we were to take all the curves and turns
out of the intestine, we would
find that it is very long.
It's approximately nine meters long.
Now, the structure of that digestive tract
turns out to be very important
in terms of gut-brain signaling.
Once again, it's a tube
and the hollow of that tube
is called the lumen, L-U-M-E-N.
But the walls of the tube
are not necessarily smooth,
at least not for significant portions
of the digestive tract.
For much of the digestive tract,
there are bumps and
grooves that look very much
like the folds in the brain,
but these bumps and grooves
are made up of other tissues.
They're made up of what's
called a mucosal lining,
so there's a lot of mucus there.
And if we were to look really closely,
what we'd find is that there are
little hairy-like cellular processes
that we call microvilli
that are able to push things
along the digestive tract.
The microbiota reside
everywhere along the lumen
of the digestive tract,
starting at the mouth and
all the way to the other end.
And they reside within those microvilli
and they reside within the lumen.
And if we were to look really closely
at the bumps and grooves
along the digestive tract,
what we would find is that
there are little niches,
little areas in which particular things
can grow and reside best.
Now, that might sound kind of gross,
but it actually is a good thing,
especially what's growing
and residing there
are microbacterial organisms
that are good for your gut
and that signal good things to your brain.
And we will talk about what
that signaling looks like
and how that's done and
accomplished in just a few moments.
But I want you to get a clear
mental picture of your gut,
something that we don't often see.
And often when we think about the gut,
again, we just think about
the hollow of the stomach,
food going in there, and getting digested,
but it's far more complex
and actually far more
interesting than that.
Now, I've been referring
to the gut microbiome
and to the microbiota and these bacteria.
Let me define those terms a
little bit more specifically
just to avoid any confusion.
The microbiota are the actual bacteria.
The microbiome is used
to refer to the bacteria
but also all the genes as bacteria make,
because it turns out that
they make some important genes
that actually impact all of us.
You have loads and loads
of these little
microbiota, these bacteria.
In fact, right now you
are carrying with you
about two to three kilograms,
so that's more than six pounds,
of these microbiota, these bacteria.
And if we were to look at
them under a microscope,
what we would see
is these are relatively
simple little organisms.
Some remain stationary
so they might plop down
into the mucosal lining
or they might hang out on
a particular microvilli
or they might be in one
of those little niches,
and others can move about,
but they basically fill the entire lumen.
They surround and kind of coat the surface
of the microvilli and they're tucked up
into any of those little niches
that are available to them
to tuck into.
If you were to take the head of a pin
and look at it under the microscope,
you could fit many, many hundreds,
if not thousands or more of
these little microbacteria.
And the reason I say many,
many thousands or more,
I'm giving a kind of broad range there,
is that they do vary in size
and, again, they vary as to
whether or not they can move
or they don't move.
Now, they're constantly
turning over in your gut,
meaning they're being born so to speak
and they're dying off.
And some will stay there
for very long periods
of time within your gut
and others will get excreted.
About 60% of your stool,
as unpleasant as that
might be to think about,
is made up of live and dead microbacteria.
So you're constantly making
and excreting these microbacteria.
And which microbacteria you make
and how many stay inside
your gut and how many leave,
meaning how many are excreted,
depends a lot on the chemistry of your gut
and depends very strongly
on the foods that you eat
and the foods that you do not eat.
Now, just because what we
eat strongly influences
our microbiome, meaning our microbacteria,
does not mean that there
are not other influences
on what constitutes our microbiome.
Our microbiome is also
made up by microbacteria
that access our digestive
tract through our mouth,
through breathing, through kissing,
and through skin contact.
In fact, one of the major
determinants of our microbiome
is who we interact with
and the environment
that we happen to be in.
And that actually includes whether or not
we interact with animals.
In a little bit, I'll talk about some data
as to whether or not you grew
up in a home that had animals,
whether or not you grew up in the home,
whether or not there was
a lot of social contact,
meaning skin contact,
or whether or not you grew up
in a more animal sparse,
contact sparse environment
and how that shapes your microbiome.
But the simple point is that what you eat
influences your microbiome,
but also what you do,
what you think, and what you feel,
and many of the low microbacteria
that get into your digestive tract
do so by way of social interactions.
In fact, if you ask a neurobiologist
what the role of the microbiome is,
they'll tell you almost certainly
that it's there to impact brain function.
But if you have friends
that are microbiologists,
such as I do, they'll tell you,
well, maybe the brain and
nervous system are there
to support the microbiome.
It's the other way around.
You have all these little microorganisms
that are taking residence in our body.
They don't really know what
they're doing as far as we know.
We don't know that they have
consciousness or they don't.
We can't rule that out, but
it seems pretty unlikely.
Nonetheless, they are taking advantage
of the different environments
all along your digestive tract.
They are taking advantage
of the sorts of social interactions,
for instance, the people you talk to
and that breathe on you,
the people that you shake hands with,
the people that you kiss or don't kiss,
the people that you happen to be
romantically involved with or not,
your dog, your cat, your lizard, your rat,
whatever pet you happen to own
is impacting your microbiome.
There's absolutely no question about that.
So hopefully now you have
some sense of the architecture
of the digestive pathway
and you have some sense of the trillions
of little microbacteria that are living
all along the different components
of that digestive pathway.
But what we haven't talked about yet,
and what I'd like to talk about now,
is what those little
microbiota are actually doing
in your digestive tract.
In addition to just living there
for their own intents and purposes,
they are contributing, for
instance, to your digestion.
Many of the genes that
those microbiota make
are genes that are
involved in fermentation
and genes that are involved in digestion
of particular types of nutrients.
And in a little bit, we will talk
about how what you eat can
actually change the enzymes
that those microbiome components make,
enzymes largely being things
that are responsible for digestion.
They catalyze other
sorts of cellular events
but in the context of
the digestive pathway,
we're talking about enzymes
that help digest your food.
So those microbiota are indeed
helping you in many ways.
And if you lack certain microbiota
that can help you digest,
it stands to reason that
you would have challenges
digesting certain types of foods.
The other amazing thing
that these microbiota do
is they change the way
that your brain functions
by way of metabolizing or facilitating
the metabolism of particular
neurotransmitters.
So one of the ways that having
certain microbiota present
in your gut can improve your
mood or degrade your mood,
for instance, is by way
of certain microbiota
being converted into or
facilitating the conversion
of chemicals, such as GABA.
GABA is what we call an
inhibitory neurotransmitter.
It's involved in suppressing the action
of other neurons.
And that might sound like a bad thing,
but all types of sedatives, for instance,
alcohol, and a lot of neurons
that naturally make GABA
can help quiet certain
circuits in the brain,
for instance, circuits
responsible for anxiety.
In people who have epilepsy,
the GABAergic neurons, as they're called,
can all often be disrupted
in their signaling,
meaning they're not
cranking out as much GABA
and therefore the excitatory neurons,
which typically release other
molecules like glutamate
can engage in what's
called runaway excitation
and that can give rise to seizures.
So the simple message here
is that the microbiota
by way of making neurochemicals
can influence the way
that your brain functions.
So you want to support those microbiota
and we will give you tools
to support those microbiota.
But the takeaway at this point
is that those microbiota
are making things locally
to help digest food.
Other microbiota are helping to make
certain neurotransmitters like GABA,
and we'll also talk about
dopamine and serotonin.
And so the very specific
microbiota that reside in your gut
have a profound influence
on many, many biological functions,
especially immune system function,
brain function, and digestion.
So that should give you
a fairly complete picture
of your gut microbiome.
Now I'd like to talk
about how your microbiome
and your brain communicate,
or more accurately, how your microbiome
and the rest of your
nervous system communicate.
Neurons, which simply means nerve cells,
are the cells that do
most of the heavy lifting
in your nervous system.
There are of course other
cell types that are important.
Glial cell, for instance, very,
very important cell types.
You have endothelial cells,
which are responsible for blood flow,
pericytes and other types of cells,
but the neurons are really
doing most of the heavy lifting
for most of the things we think about
in terms of nervous system function.
You have neurons in your gut
and that should not surprise you.
Neurons reside in your brain,
your spinal cord, your eyes,
in fact, all over your body,
and you've got them on your
heart and in your heart,
and you've got them in your lungs,
and you've got them in your spleen,
and they connect to all
the different organs
and tissues of your body.
So that's not surprising that
you have neurons in your gut.
What is surprising, however,
is the presence of
particular types of neurons
that reside near or in the mucosal lining
just next to that lumen of the gut
and that are paying attention,
and I'll explain what I
mean by paying attention,
to the components of the
gut, both the nutrients
and the microbiota,
and thereby can send signals
up to the brain by way of a long wire
that we call an axon, and can communicate
what the chemistry and what
the nutritional quality
and what the other aspects of
the environment are at the gut
at a given location up to the brain
in ways that can influence
the brain to, for instance,
seek out more of a particular food.
Let me give you a sort of
action-based picture of this.
Let's say like most people,
you enjoy sweet foods.
I don't particularly enjoy sweet foods
but there are a few that I like.
I'm a sucker for a really
good dark chocolate
or really good ice cream
or I got this thing for donuts
that seems to just not quit
although I don't tend to
indulge it very often,
I do like them.
If I eat that particular food,
obviously digestion starts in the mouth.
There are enzymes there,
it gets chewed up,
the food goes down into the gut.
These neurons are activated,
meaning that causes the neurons
to be electrically active
when particular components,
certain nutrients in
those foods are present.
And for the cell types,
or I should say the neuron
types that matter here,
the nutrients that really
trigger their activation
are sugar, fatty acids,
and amino acids.
Now, these particular neurons
have the name enteroendocrine cells
but more recently they've been
defined as neuropod cells.
Neuropod cells were discovered
by Diego Bohorquez's
lab at Duke University.
This is a phenomenal set of discoveries
made mostly in the last 10 years.
These neuropod cells, as I mentioned,
are activated by sugar,
fatty acids, or amino acids,
but have a particularly
strong activation to sugars.
They do seem to be part of
the sweet sensing system.
And even though I'm focusing
on this particular example,
they represent a really nice example
of how a particular set
of neuro cells in our gut
is collecting information
about what is there
at a particular location in the gut,
and sending that
information up to our brain.
Now, they do that by
way of a nerve pathway
called the vagus nerve.
The vagus nerve is part of
the peripheral nervous system.
And the vagus nerve is a
little bit complex to describe
if you're just listening to this.
If you are watching this,
I'll try and use my hands as a diagram
but really the best thing to do
if you want really want
to learn neuroanatomy
is to just imagine it in
your mind as best you can
and if you can track down
a picture of it, terrific,
but here's how it works.
Neurons have a cell body
that we call a soma,
that's where all the DNA are contained.
That's where a lot of
the operating machinery
of the cells are contained
and a lot of the
instructions for that cell
of what to be and how to
operate are contained.
The cell bodies of these
neurons or the relevant neurons
are actually up near the neck.
So you can think of them
as a clump of grapes,
'cause cell bodies tend
to be round or oval-ish.
And then they send a
process that we call an axon
in one direction out to the gut
and they'll send another
process up into the brain.
And that little cluster near the neck
that's relevant here is called
the nodose ganglion, N-O-D-O-S-E.
The nodose ganglion is a
little cluster of neurons
on either side of the neck.
It has a process that goes out to the gut
and a process that goes up into the brain.
And again, these are just one component
of the so-called vagus nerve.
The vagus nerve has many, many branches,
not just to the gut.
There are also branches to the liver,
branches to the lungs,
branches to the heart,
branches to the larynx,
and even to the spleen,
and other areas of the
body that are important.
But right now we're just
concentrating on the neurons
that are in the gut that
signal up to the brain.
And what the Bohorquez lab has shown
is that these neuropod
cells are part of network.
They're sensing several
different nutrients,