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- 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 sugar,
in particular, how our
nervous system regulates
our sugar intake and our
are seeking of sugar.
We're also going to discuss how sugar
regulates our nervous system.
And as you'll soon learn,
sugar really impacts our brain and body
by two main mechanisms.
One of those mechanisms is based on
the sweet taste of sugar,
which itself is rewarding.
Even if you're not much of a sweet tooth,
I confess I'm not,
most people enjoy sweet tastes
more than bitter tastes.
And the sweet taste of
sugar and its various forms,
is strongly reinforcing,
meaning it triggers the
activation of neurons,
nerve cells in the brain and body,
that make us want to consume
more of that sweet substance.
Incidentally, sweet tastes also
make us want to eat more of
other substances as well.
You may be familiar with that phenomenon.
Now sugar also triggers
mechanisms in the brain and body
based on its nutritive content,
independent of its sweetness.
What that means is that
the actual caloric content
and the way that sugar interacts
with your nervous system
at a subconscious level,
without your awareness,
also impacts your craving and seeking
of sugar and other foods.
Today, we are going to
discuss what happens
when you ingest sugar in
terms of your body's reaction
and your brain's reaction.
We are also going to
talk about what happens
when you don't ingest enough sugar.
'Cause it turns out sugar
is such a powerful fuel
for the brain
that under conditions
where people don't ingest
enough sugar, or where their
so-called blood glucose,
which is basically blood
sugar of a particular form
gets too low, their neurons
don't function as well.
That said, there are conditions
of very low blood sugar
in which neurons can function even better.
So today we are going to
talk about the ins and outs,
the ups and downs of sugar
as it relates to your nervous system.
And by the end of this episode,
I'm confident that you
have a much clearer picture
as to how much sugar
you should be ingesting,
whether or not you should avoid sugars
that you're currently eating,
and you will certainly
understand much, much more
about the energy and fuel sources
that your brain relies on,
which I'm certain will allow you to make
better informed choices about
the foods you eat and avoid
toward mental health, physical
health, and performance.
I'm pleased to announce that
I'm hosting two live events
this May.
The first live event will be
hosted in Seattle, Washington
on May 17th.
The second live event will be hosted
in Portland, Oregon on May 18th.
Both are part of a lecture series entitled
The Brain-Body Contract,
during which I will discuss
science and science based tools
for mental health, physical
health and performance.
And I should point out that
while some of the material
I'll cover will overlap with
information covered here
on the Huberman Lab Podcast,
and on various social media posts.
Most of the information I will
cover is going to be distinct
from information covered on
the podcast or elsewhere.
So once again, it's Seattle on May 17th,
Portland on May 18th,
you can access tickets by
going to Hubermanlab.com/tour.
And I hope to see you there.
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 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 Thesis.
Thesis makes what are called nootropics,
which means smart drugs.
Now, to be honest,
I am not a fan of the term nootropics,
I don't believe in smart drugs
in the sense that I don't believe
that there's any one substance
or collection of substances
that can make us smarter.
I do believe, based on science, however,
that there are particular neural circuits
and brain functions that
allow us to be more focused,
more alert, access creativity,
be more motivated, et cetera.
That's just the way that the brain works,
different neural circuits
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And so the idea of a nootropic
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all around,
fails to acknowledge that
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These are all different brain processes.
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And as far as I know they're
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They only use the highest
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Some of those I've talked
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My go-to formula is the Clarity Formula,
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That's takethesis.com/huberman
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Today's episode is also brought to us
by Athletic Greens, now called AG1.
Athletic Greens is an all in one
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I've been taking Athletic
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so I'm delighted that they're
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The reason I started
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It makes up for any
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In addition, it has probiotics,
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I've done a couple of
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With Athletic Greens, I
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Today's episode is also
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Okay, let's talk about sugar,
let's talk about how
sugar impacts your brain,
and how your brain impacts
your pursuit or your avoidance
of sugar.
Let's get a few things
out of the way first.
The first thing is that there's nothing
inherently bad about sugar.
I know the word sugar
gets a bad rap nowadays,
and indeed, you're going to
hear over and over again,
during this podcast,
that consuming a lot of refined sugars,
in particular high fructose corn syrup,
is known to have a very
large number of bad effects
on the brain and body.
I don't know that there's anyone
that really debates that anymore.
Even if we just agree, and
I think we should all agree,
on the so-called calories in,
calories out principle, right?
It's a principle thermodynamics
that if we ingest more
energy than we burn,
we are going to gain weight.
If we ingest less energy than we burn,
we are generally going to lose weight.
And if the two things are in balance,
ingestion and burning of energy,
well, then we're going to maintain weight.
So everyone agrees on
that, I agree on that.
But beyond, there are a number of ways
in which particular nutrients,
in the case of today's episode, sugar,
impact the way that the brain works,
such that we tend to seek out
more of particular nutrients.
For instance, if we eat sugar,
there are two, or at least two mechanisms,
by which we will crave more sugar.
I think most people are
aware of that experience,
but today I'm going to explain
exactly how that works.
But also that when we ingest sugar
it has a bunch of different effects
on the way that our neural circuits work
that can allow us to be
more or less focused,
more or less agitated,
a more or less happy,
more or less depressed in some cases.
So today, as we explore this
thing we're calling sugar,
we are going to explore
that mainly in the context
of the nervous system,
but also in the context of how
the nervous system regulates
many, many functions and behaviors
that are important to all of you,
your ability to think,
your ability to extra size,
your ability to gain weight, lose weight,
whatever your goals might happen to be,
sugar plays a critical role
in achieving those goals.
And in some cases,
if you're ingesting too
much at the wrong times
or the wrong forms, sugar can
actually impede those goals.
In fact, sugar can prevent
all the right behaviors
from allowing you to achieve
the goals that you want.
So today we are going to place sugar
into its proper context.
The way I want to start off by doing that
is to tell you a little bit
of what happens when we eat
and a little bit of what the brain does
to respond to those events.
So what happens when we eat?
Well, I've done an entire
episode on metabolism.
So if you're interested
in the full cascade
of hormonal and neural events
that occurs when we eat,
please check out that episode.
But for the sake of today's discussion,
let's just take a, what
I call top contour view
of the hormonal response
to ingesting food.
Now, anytime we eat,
that is the consequence
of a number of things
that happened before we ate.
There's a own in our
brain body called Ghrelin,
spelled G-H-R-E-L-I-N.
Ghrelin is a hormone that increases
depending on how long it's
been since we ate last.
So the longer it's been
since we had a meal,
Ghrelin levels are going to be
higher and higher and higher,
and it essentially makes us hungry
by interacting with particular neurons
in an area of the brain called
the arcuate nucleus of the hypothalamus
and some other areas as well,
like the lateral hypothalamus.
You don't need to know the
names of those brain areas,
but if you'd like to
know them, there they are
Ghrelin increases, it
tends to make us hungry.
And then when we eat,
typically what happens is
Ghrelin levels go down.
So it's a very logical system.
Now, when we eat, assuming
that we eat carbohydrates,
but even if we just eat
some protein and some fats,
we will experience a
slight, or in some cases,
a large rise in blood glucose,
blood glucose is simply blood sugar.
And the body and brain, we
should say in particular,
the nervous system doesn't function well
if blood sugar is too high or too low.
So as a consequence, we
have another hormone,
which is released from the pancreas,
which is called insulin,
which helps regulate the amount of glucose
in the bloodstream.
So even if you were to
ingest an entire cup,
an eight ounce cup of pure table sugar,
which would send your blood
glucose very, very high,
assuming that you have a
normal insulin response,
that you're not diabetic,
that insulin response would help clamp
that blood glucose level
so that it did not cause
damage to your brain and body.
Because if blood sugar goes too high,
it's actually toxic to neurons
and other cells of your body,
it can kill them off.
And neurons of the central nervous system,
meaning the brain and spinal cord,
once they are dead, they do not come back.
So your biological systems understand this
at a biological level that is,
and prevent that death of
cells due to high blood sugar,
by keeping insulin around,
in order to clamp blood glucose.
Diabetics, we call them
type one diabetics,
who don't make insulin,
have to take insulin when
they eat in particular,
when they eat foods that
raise their blood sugar,
specifically to avoid that neurotoxicity
and the other deleterious
effects of high blood sugar.
So Ghrelin is a hormone that goes up
the longer it's been since we've eaten,
it tends to stimulate hunger.
When we eat, Ghrelin is suppressed.
Blood glucose typically goes up,
especially when we eat a
carbohydrate containing meal.
When blood glucose goes up,
it's regulated in the body,
meaning its peaks and its valleys
are more or less smoothed out,
and that glucose is sequestered,
it's taken away where it
needs to be taken away.
And in certain locations,
it's delivered to cells
so that those cells can use the glucose.
Now, one of the chief organs
for glucose utilization
is the brain,
neurons are tremendously
metabolically active.
And their preferred mode of metabolism
is glucose metabolism.
In other words, neurons
basically run on sugar,
which is not to say that you
should eat a lot of sugar.
As you'll see today, there
are states of mind and body,
for instance, fasted states,
in which people report
having immense amounts
of mental clarity and their blood glucose
is actually quite low.
So it is simply not the
case that the more sugar
that you ingest, the better
that your brain will function.
But it is the case that for most people,
meaning people who are not on a ketogenic
or very low carbohydrate diet,
they're not adapted to
low carbohydrate diets,
that neurons in their brain and body
are using glucose in order to function.
That's what allows those neurons
to fire electrical potentials,
that's how we refer to it,
firing, meaning sending electrical
signals down their length
to communicate with other neurons.
To illustrate just how
important glucose is
for brain function,
I'd like to describe a study
that just recently came out,
that sits on a long
history of similar studies.
But the one that just came out
is particularly interesting.
Now I want to point out
that, unless I say otherwise,
I'm going to refer to typical diets,
meaning I have to believe
that most people out there
are in ingesting some starch
some starch or carbohydrate.
I do realize there are people following
very low carbohydrate diets
or moderately carbohydrate diets.
I even know that there's
some folks out there
who are on the so-called carnivore diet,
they only eat meat and
organs, maybe a little fruit.
But I'm going to assume
that the vast majority
of people listening ingest
proteins and carbohydrates.
So unless I say ketogenic, or
I emphasize ketosis itself,
which I will,
I'm referring to a kind of typical diet
where people are consuming fats,
proteins and carbohydrates.
I count myself as one such individual.
At some point I might try the
carnivore diet, who knows,
I might I a pure vegan diet, who knows.
But for my entire life up
until now, I'm 46 years old,
I've been a proud omnivore,
meaning I've tried to eat
high quality as much as I can,
unprocessed foods,
I try and really avoid
highly processed foods.
But I do eat from those
three macronutrient groups,
proteins, carbohydrates, and fats,
and I'm going to assume
that most of you do as well.
The study I'd like to emphasize,
recorded from neurons, nerve cells,
in the brain, in particular
in the part of the brain
`that responds to visual images,
the so called visual cortex.
And neurons in the visual
cortex are beautifully tuned,
as we say, to particular
features of what we see.
The primary example of this,
the kind of classic example,
is if you put a little
electrode next to a neuron
in your visual cortex,
or if we put you into
an FMRI scanner machine,
which can detect neural activity,
and I were to show you a
bunch of just little lines,
bars of light, they could
be dark bars of light,
they could be light bars of light,
on a screen in front of you.
So some would be vertical,
some would be horizontal,
some would be at 45 degrees,
what we would see is that
some neurons respond best,
meaning they fire a lot
of electrical activity
to vertical lines,
other ones respond to horizontal lines,
and others respond to 45 degree lines.
And this so called orientation tuning,
meaning because of the
orientation of the line,
is a cardinal classic feature of the way
that your visual system is built.
And everything that you see,
whether it's a face or a
dog or a cat or a landscape,
is built up from these very
simple neuron responses.
In other words, when you look at a face,
there are neurons deep in the
brain that respond to faces.
But the only reason that those neurons
can respond to those faces
is because they receive
signals from neurons
in your visual cortex.
Some of which respond to vertical lines,
some of which respond to horizontal lines,
and some which respond to 45 degree lines.
And all of those are built up
in what we call a
hierarchical representation,
which just fancy language for
those are the building blocks
by which you see a face
and you recognize a face.
And it's really an amazing phenomenon,
it happens very, very fast.
You never notice that you're doing this,
but everything is built up from these
fundamental orientation-tuned neurons.
Now orientation-tuned
neurons are so fundamental
that they are the building blocks
by which you make up all
other things that you see,
it's the way you read,
it's the way that you recognize
faces, as I mentioned,
and everything else.
Experimentally, it's quite straightforward
to measure how sharply tuned
one of these neurons is.
In other words, if I were
to show you a vertical line
and find a neuron in your brain
that responds to vertical lines,
I could also ask whether
or not that neuron fires
any electrical activity
in response to a line
that's not quite vertical,
maybe just 10 degrees off
vertical or 20 degrees
or 30 degrees.
And what I eventually would
find is that that neuron
was orientation-tuned over a
particular range of angles.
It's not only going to
respond to vertical lines,
it's also going to respond to lines
that are about 10 degrees
off vertical on either side,
but probably not much more, maybe 20,
but usually it's going to
be anywhere from vertical
to just tilted slightly.
In the recent experiment
that was published
in the journal, "Neuron,"
Cell Press journal,
excellent journal,
the authors asked a really
interesting question,
they asked whether or not
the sharpness of tuning,
the precision of orientation
tuning of these neurons
is dependent on blood glucose level.
So just to cut to the chase,
to give you the answer,
what they found is that
when subjects are well fed,
neurons that responded to vertical,
responded very strongly to vertical,
but not very much at all to other angles,
of what we call stimuli,
so lines that are 10
degrees or 20 degrees off.
If they looked at neurons that
were primarily tuned, right,
that preferred horizontal lines,
they found the same thing.
So it wasn't something
unique to vertical lines.
What they basically
found was the sharpness,
the precision of tuning
of neurons in the brain,
was best when subjects were fed.
And conversely, when subjects were fasted,
the orientation tuning of these
neurons became much broader.
What it meant was that a neuron
that normally would
only respond to vertical
now responded to other
angles of lines as well.
You might say, well, that's great, right,
these neurons that at one
point could only do one thing
are now tuned to other things.
But it's not so great
because what that means
is that in the fasted state,
your perception of the outside
world is actually distorted,
it's blurred, it's not as
precise as it is when you're fed.
And when I say fed,
what I really mean is when
glucose is available to neurons.
Now, for some of you, maybe many of you,
and including myself,
intermittent fasting,
or some variant thereof, is
actually a state that I like.
It allows me to focus.
For instance, as I mentioned before,
and even earlier in this podcast,
I tend to eat my first meal
sometime around 11:00 AM.
And then I generally eat my last meal
sometime around 8:00 PM,
plus or minus an hour
on either side, I'm not
super strict about it.
And occasionally I'll
wake up really hungry
and I'll eat something before 11:00 AM.
I'm not super strict about this
intermittent fasting thing.
It just seems to be how
my appetite works best,
given my schedule, et cetera.
In the morning, I tend to be most focused.
And I always associated that with the fact
that I was fasted.
I ingest water and some caffeine about
90 minutes after waking
up, I drink my caffeine,
but I hydrate from the time I
get up, et cetera, et cetera.
And I know a lot of other people
have had the experience of being fasted
and feeling like they have
a lot of mental clarity.
When you are in a fasted state,
typically you are going to use fuels
that are available to the neurons,
based on your intake
of food the day before,
maybe you're using some glycogen,
maybe you're using some fat,
maybe you're using some blood sugar,
that's derived from other
storage sites in the body.
You don't actually use
fat as a fuel source
for neurons under typical conditions.
But there are ways in
which proteins and fats
and glycogen, et cetera,
are converted into fuel
that neurons can use.
What's interesting about this study
is that the study says that when well fed,
meaning when blood glucose, sugar,
is at a properly elevated
level in the bloodstream,
it can be delivered to the brain
in a way that allows neurons to work best,
which is really all just
to underscore the point
that I made earlier,
which is that your nervous system
is extremely metabolically
demanding, and it loves glucose,
neurons love glucose.
So the takeaway from this study
is not that you should avoid fasting,
the takeaway from this study
is that there are elements
of the fasted state
in particular the elevations in things
like epinephrine and norepinephrine,
also called adrenaline and noradrenaline,
that can give us this
kind of clarity of mind
that many people are
pursuing when they fast.
That's kind of one of the
reasons a lot of people fast,
they like the way that they
feel, mentally and physically.
But I think it's only fair to point out
that glucose is the preferred
source of fuel for the brain.
And this study that I mentioned
is one of many studies
that have explored how nutritional status
or blood glucose status
in the brain and body
influence neuronal tuning
and neuronal function.
And it really points to
the fact that ultimately,
your brain as an organ, is
a glucose consuming machine.
Now, when you eat a food,
that food is broken down and
if it contains carbohydrates,
it's going to be converted into glucose.
And that glucose can't get
directly into the brain
as a fuel source.
It actually has to be carried across
the so-called blood
brain barrier, the BBB,
and the actual metabolism of glucose
and the delivery of the
glucose to the neurons
is carried out by a different cell type.
And it's a cell type that
you should all know about
because it's the most abundant
cell type in your brain,
and maybe even in your
entire nervous system,
and that's the so-called astrocyte.
Astrocytes are one of
several types of glia,
the word glia means glue.
But many people have taken
that name, glia, glue,
to think that, oh,
the only thing that the
astrocytes are doing
is just kind of holding things together.
Actually, the astrocytes
are involved in delivering
glucose to the neurons,
they are critically involved in shaping
your neuronal function
and brain plasticity,
the brain's ability to change
in response to experience.
So these astrocytes are like the little
waiters and waitresses
bringing glucose to the neurons
and the neurons are going
to do the heavy lifting
that's involved in perception
and behavior and action.
So if prior to this episode,
you didn't already realize
that glucose, blood sugar,
is vital to the function of your brain
and other neurons of your
nervous system, now you know.
And for those of you that have experienced
the increase in mental clarity
that comes after a properly
timed, properly composed,
meaning it has the right
macronutrients in the right ratios,
and a properly sized meal,
well then now you have justification
for eating something as
a way to improve the way
that your brain works.
It turns out that your
brain is going to work best
when it's got glucose available,
whether you like to fast or not,
that's just the reality of things.
The same thing is also true
for the neurons in your body.
The way that you are able to
move the limbs of your body,
the way you are able to perform exercise
or movement of any kind for that matter,
is because as neurons,
called motor neurons,
send electrical potentials
to the muscle fibers,
they release a neurotransmitter
called acetylcholine,
which causes contraction
in the muscle fibers,
and allows you to move your limbs.
Those neurons are also very
metabolically demanding,
especially when you're doing
demanding types of physical work,
and that could be cycling
or running or weightlifting
or yoga or whatever it may be.
Those neurons require a ton of glucose.
If you've ever had the
experience of having to
think very hard about how
you're generating a movement
or force yourself to continue
to endure in a given exercise,
you might have thought,
oh, you know, I'm running out of fuel,
that's why I'm getting
tired, it's hard to do.
That's actually the case sometimes,
but that's not always the case.
One of the reasons that it feels like work
is because your so called
upper motor neurons,
the ones that control
the lower motor neurons
in your spinal cord, which
control your muscles,
they have to be very metabolically active.
It's one thing to engage
in a reflexive movement
where you're just walking around
or if you're running continuously.
But when you suddenly have to
focus on what you're doing,
and you have to generate specific patterns
of motor movement,
well, that feels demanding because one,
it increases the release of adrenaline
in your brain and body,
which makes you feel a little
bit agitated and more alert,
but also deliberate thought,
deliberately controlling the way
that your brain and body is moving,
requires more glucose uptake,
more energy in those very neurons.
And this is also why after
doing a long about of exercise,
you might be tired,
but also if you do a about of
skill learning of any kind,
or if you've been reading
and thinking about
what you're reading,
or if you had a intense
conversation with somebody
where you're really
forcing yourself to listen,
and hopefully they're
listening to you too,
and you're really trying to
parse what they're saying,
and maybe you're doing that right now,
and you're trying to really
track something, that's work,
and that work requires
glucose uptake by neurons,
both in the brain and in your body.
Now that we've established that glucose
is the preferred source of
fuel for the nervous system,
I'd like to concentrate on
a few of the other types of
sugars that we ingest on a common basis,
and the impact that those have
on brain function and body function.
I'd particularly like
to focus on fructose.
Fructose, of course, is found in fruit,
it's also found in the infamous
high fructose corn syrup,
which we will talk about today.
It's worth pointing out
that the concentrations
of fructose in fruit
is quite low compared to the
concentrations of fructose
in high fructose corn syrup.
High fructose corn syrup is
approximately 50% fructose,
which turns out to be
an enormously high percentage
of anything, really,
especially when we cut contrast that
to the concentrations
of fructose in fruit.
Fruits have other types
of sugars in them as well.
You know, the sucrose
content of most fruit
and fruit juices is low.
Although there are some
fruits like melons, peaches,
pineapples, and so forth,
that contain a little less
than 10% or so of sucrose.
Things like mangoES can
have a lot of sucrose.
But typically the amount of fructose,
fructose, I think is the
proper pronunciation,
people are always correcting me.
Fructose is anywhere from
1% to about 10%, right?
It's really going to vary quite a bit.
And many of you have probably heard
of the so-called glycemic index,
which is basically a measure
of how fast blood sugar rises
after eating particular foods, et cetera.
We're going to set aside
the glycemic index for now,
we will come back to it.
It has some relationship
to the concentrations
of fructose in fruit.
But the point that I'd like to make
is that fructose as a sugar,
is handled very differently
in the body than is glucose.
But I also want to emphasize that
because the percentage of
fructose in fruit is rather low,
especially compared to
high fructose corn syrup,
many people have demonized fructose
saying that fructose makes you fat,
or that fruit makes you fat.
If you look at the data,
that's not really the case.
The fact of the matter is that
the concentrations of fructose in fruit
are so low that unless someone
is consuming a lot of fruit,
or they're consuming a lot of fruit
on the backdrop of a highly processed diet
or a diet that has a lot of other stuff
that they might not want to be ingesting,
you can't really say that
fructose is fattening.
I don't really think that
there's any basis for saying that
fructose itself is bad.
Now high fructose corn
syrup is a different issue,
and too much consumption of
anything, fructose included,
whether or not it comes
fruit or otherwise,
can be a problem for
the ways that it impacts
the neural circuits that process sugar,
not just glucose, but fructose.
And so we'll illustrate those
neural circuits in a bit,
and it'll become very clear to all of you,
regardless of whether or not
you have a background in
biology or metabolism,
nutrition, or otherwise,
why ingesting very high
concentrations of fructose
is not going to be a good thing
for the way that your brain functions.
One of the key distinctions
between glucose and fructose
is that fructose most likely
cannot directly access the brain.
It actually needs to be converted
into glucose in the liver.
And the way that conversion occurs
feeds back to a set of
hormones and neural pathways
that we talked about earlier,
which have a lot to do with appetite.
And to just summarize what is
now a lot of very solid data,
fructose and specifically fructose,
has the ability to reduce
certain hormones and peptides
in our body whose main job
is to suppress Ghrelin.
As you recall, Ghrelin is
a hormone that increases
the longer it's been since we've eaten,
and Ghrelin makes us hungry
by stimulating particular
neurons in our hypothalamus,
it actually makes us really want to eat.
And in particular, really
makes us want to eat sugary
and fatty foods.
Fructose reduces the
activity of the hormones
that reduce Ghrelin .
And so the net consequence of that
is that fructose increases Ghrelin.
So, although I and I think
pretty much everyone out there,
say for a few individuals,
agrees that calories in and calories out
is the fundamental
principle of weight loss,
weight maintenance or weight gain.
Ingesting fructose shifts
our hormone system,
and as a consequence, our neural
pathways within our brain,
the hypothalamus,
to be hungrier regardless of
how many calories we've eaten.
Now I also want to be absolutely clear,
this does not mean that eating
an apple or eating a melon
or eating a couple of
apricots or something
is going to make you hyperphagic,
meaning it's going to
make you just want to
eat, eat, and eat, that's
simply not the case.
But if you compare fructose
and you compare glucose,
not only are they metabolized differently
in the brain and body,
but in addition to that,
fructose has this impact
of reducing the hormones
that reduce hunger hormones
in neural circuits.
And so fructose does
have this kind of twist
in its phenotype, right?
Or I guess if fructose
had a dating profile,
this would be a kind of a
red flag in that profile,
because fructose itself,
while it's actually a pretty
good fuel source in many ways,
and it's often packaged
in things like fruits,
which bring along fiber
and vitamins and minerals,
that I think for many of us are things
that we should be eating more
of and ingesting more of,
it can suppress the pathways
that suppress hunger.
And as a consequence,
it can increase hunger.
So current recommendations for most people
are to eat more fruits and vegetables.
But for those of you that are
trying to control your hunger,
ingesting a lot of fruit to
is probably not going to be
a good idea.
Certainly, ingesting it from
high fructose corn syrup
is not going to be a good idea
because of the enormous
percentages of fructose
in high fructose corn syrup,
50%, or sometimes even more.
But even from fruit,
some people will find that fruit
really quenches their appetite.
Other people will find that
fruit stimulates their appetite.
And I suppose if you're trying
to stimulate your appetite,
then ingesting more fruit
might actually be advantageous
to you.
So fructose provides a bridge for us
between a particular kind
of sugar, hormone function,
in this case Ghrelin and the hypothalamus.
which leads us to the next question,
which is what is it about sugar
that makes it such an
attractive thing for us?
Why do we like it so much?
And the obvious answer that
most people arrive at is,
well, it just tastes really, really good.
But that's actually not the way it works.
The rewarding property
is as we say of sugar,
whether or not they come in
the form of sucrose or fructose
or foods that increase
glucose to a very high level,
actually is not just related
to the taste of the foods
that produce that elevation
in glucose, sucrose, or fructose.
It is in part, but that's
only part of the story,
and the rest of the story,
once you understand it,
can actually place you in a
position to much better control
your sugar intake of all kinds,
but also your food intake
in ways that can allow you
to make much better choices
about the foods you ingest.
And actually at this point,
I should probably give a confession,
I've said today, and I'll say it again,
and I've said it I'm pretty podcast.
I don't have much of a sweet
tooth and indeed that's true.
And I can kind of pass
on chocolate or ice cream
or things like that,
it seems like with each successive year,
sweet things are less
and less appealing to me.
Of course, savory foods,
anything that is really fatty,
salty, savory, those don't
last long in my presence,
but I always say, I don't really
like sweet things so much,
and I like sweet people,
but I don't tend to like
sweet foods, which is true.
But there's probably one
exception and that's mangoes.
And it turns out that mangoes
have the highest percentage
of sugar in them,
in particular fructose, as
well as other forms of sugars.
So what I do, because
I love mango so much,
is I will have mangoes
probably twice a week,
but I'll have them after some
sort of resistance training
or hard run or something like that.
Because it is the case that
after you exercise hard,
in particular exercise that is
of the high intensity variety,
that your body is more efficient
at using circulating sugar.
It's able to store that
or use that for fuel.
And so what I'll typically
do is just take the mango,
I actually eat the peels too.
I know there probably some
people are going to cringe
when they hear that,
I find them delicious.
So I'll just bite into
those things like apples,
I don't eat the pits, however.
So now I want to take us on a journey
into the nervous system to explain,
the pathways in the brain and body
that regulate our appetite for sugar.
Now, keep in mind what I
already told you before,
which is that when we ingest foods,
they're broken down
into various components
and glucose is going to
be shuttled to the brain,
and of course, to other
neurons in our spinal cord
and elsewhere, and to our muscles, cetera,
in order for all of those
cells and organs and tissues
is to be able to function.
The fact that so many cells
and organs and tissues
require glucose in order to function
has led to a situation where you have
dedicated neural machinery,
pieces of your brain,
that are almost entirely,
if not entirely devoted,
to seeking out of sugar or
foods that contain sugars.
And to make sure that you
not only seek those out,
but you know where those foods are
and that you ingest more
and more and more of them.
And there are two main ways
that these neural circuits work.
In fact, we can see that
there are two neural circuits
entirely that work in parallel.
And this is a common theme
throughout the nervous system,
and that's parallel pathways.
Parallel pathways are the
ways that you can distinguish
light from dark,
parallel pathways are
the ways that you can
distinguish high pitched
sounds from low pitched sounds,
parallel pathways are the ways
that you can flex your muscles
versus extend your muscles.
For instance,
if you move your wrist
closer to your shoulder,
you're flexing your bicep and
you're actually inhibiting,
you're actually preventing
the action of your tricep.
If you move your wrist
away from your shoulder,
you are essentially using
your extensor, your tricep,
and you're inhibiting the
activity of your bicep.
So for every function in your body
that you might think is
controlled by one brain area
or one neural circuit,
almost always there are
two or more so called
parallel pathways that ensure
that that particular behavior happens.
Now, in the case of sugar consumption,
the two parallel pathways
involve one pathway
related to the actual taste
and the perception of taste
that lead, not just you,
but every animal that we're aware of,
to seek more sweet containing foods.
The other parallel pathway
is related to the nutritive
component of sweet foods.
Meaning the degree to which a given food
will raise blood glucose.
I want to repeat that.
One pathway in your brain
and body is devoted to
getting you to seek out
sweet tasting things
that you perceive as sweet,
and another parallel pathway is devoted
to getting you to seek out foods
that lead to increases in blood glucose.
It just so happens that the foods
that lead to big
increases in blood glucose
typically are associated
with that sweet taste.
Now, this is distinctly different
than the neural pathways
that control seeking
of savory foods or salty
foods or spicy foods,
for that matter, or bitter foods.
The sweet pathway is what
we would call hardwired.
It exists, as far as we
know, in every mammal,
it even exists in fruit
flies, hence fruit fly.
Basically getting sweet
stuff into the body
might seem like it has a
lot to do with the taste,
but it has just as much to do
with the nutritive components
that sweet tasting foods carry,
and the fact that your nervous system
and so many cells in your
brain and body run on glucose.
If you recall earlier, I said,
even if you ingest fructose,
fructose can be converted
into glucose in the liver.
And I mentioned, of course,
that fructose may actually
work directly on the brain,
that's still unclear for humans,
the jury's still out on that, we will see.
But the fundamental
thing to understand here
is that when you think you
want a piece of chocolate
or you think you want a piece of cake
or you're craving something sweet,
you are both craving the taste
and your neurons are literally craving
the nutritive components
that arrive with that taste.
And simply by understanding that
can allow you to circumvent
some of the sugar cravings
that you might otherwise be a
complete hopeless victim to.
Also in this episode,
I will talk about ways
that you can sort of undermine
or short circuit these
circuits, if you will,
in order to reduce sugar
cravings on a regular basis,
if that's your goal.
Two parallel pathways,
one of the parallel pathways
has to do with conscious perception.
So animals of all kinds
of mice, rats and humans,
will prefer sugary taste
to non-sugary taste.
When we eat something that tastes sweet,
we register that sweet taste
by way of sweet receptors,
literally little ports
or portals of neurons
on our tongue and on our pallet,
a lot of people don't realize this,
but there are a lot of taste
receptors on the soft pallet
and around the mouth, on
the sides of the mouth.
So you're actually tasting things,
not just with your tongue,
but with your entire mouth
and your pallet.
So when you ingest something sweet,
very quickly there are signals
sent from those neurons
in your mouth to brain areas
that cause you to seek out
or at least pay attention to,
the source and the abundance
of those sweet things.
They literally change your perception.
In fact, there are beautiful
neuroimaging studies
that show that when people
ingest a sugary drink,
their perception of images
of foods change very much
to make those foods
appear more appetizing,
and not just foods that contain sugar.
Results of those studies do show
that there's an increase for instance,
in the perception of detail
and images of ice cream,
after you ingest a sweet drink
or even if you put like a
hard candy into your mouth,
it will make you seek
out sugary things more,
it will make sugary things
look more appetizing,
but also other foods, more appetizing.
So I think it's important that
people recognize that fact,
that when you have a
sweet taste in your mouth
or when you've tasted something
sweet within your mouth,
I should say, your perception
of has immediately shifted.
These are fast neural pathways.
We'll get into some of the
brain structures in a moment,
but these are fast neural pathways
that shift your entire self
toward seeking more sugary stuff
and more food generally.
Now, does that mean that
you should never ingest
anything sweet?
No, certainly I'm not saying that,
everyone has to decide for themselves
what the appropriate
amount of sugar intake is,
but I find it remarkable when people say,
oh, you know, I need to get my sugar fix,
or I need to have my chocolate,
or I need to have a
little bit of something
to just kind of take care
of that sugar appetite.
Because in taking care
of that sugar appetite,
maybe for the very disciplined of you,
you can just have that
one piece of chocolate
and it's great, and you can relish in it,
but it does shift the
way that you perceive
other foods as well.
And the way it does that is through our,
probably if you're listener
this podcast, now old friend,
but incredible neuro modulator, dopamine.
Dopamine is a molecule
that is released from
several places in the brain.
There's a so-called
mesolimbic reward pathway,
which is a whole set of places
in the brain or circuits,
designed to get us motivated and craving
and in pursuit of things.
And then of course there
are areas of the brain
that are involved in movement
that are linked up with those
areas involved in motivation.
That makes perfect sense.
Why would you have a brain
area involved in motivation
if you couldn't actually do
something with that motivation?
So the way that your brain is designed
is when there's an increase in dopamine,
in the mesolimbic reward pathway,
there are signals sent
to an area of the brain
called the striatum,
we're going to spend a
little bit of time today
in the striatum.
It's got a dorsal part,
meaning in an upper part
and a ventral part,
which means a lower part.
And the dopamine sent to those area,
places us, excuse me,
into modes of action,
to pursue particular things.
Sugar or sweet tastes, I should
say, to be more specific,
have an incredibly potent ability
to activate dopamine release
within the mesolimbic reward pathway.
This has been shown over
and over and over again
in animal models and in humans.
This is especially true, I should mention,
through the ingestion of sweet liquids.
Now this becomes a very
important point to us
a little later on when we
talk about the proliferation
of sodas and sweet drinks,
and dare I even say,
non-sugar or diet sodas,
we're going to get into
that a little bit later.
They are perhaps one of
the most third rail topics
in nutrition.
But when we ingest something sweet,
the perception of that sweet taste
increases dopamine in the
mesolimbic reward pathways,
which then are conveyed to
pathways for motor behavior,
and in general, place us
into modes of focused action
toward getting more of whatever was sweet.
Again, for those of you
that are very disciplined,
you can probably eat that
one piece of chocolate
and be just fine.
But if you understand the
way that dopamine works,
what you'll realize is that
when this dopamine pathway
is triggered,
it tends to create not the
sensation or the perception
of satiety, of feeling
like something is enough,
but rather to produce the
sensation of wanting more.
As described in the episode that I hosted
with my phenomenal colleague
from Stanford School of
Medicine, Dr. Anna Lembke,
she's an expert on addiction
and dopamine pathways,
the dopamine circuits of the brain
have what we call a pleasure pain balance.
And there I'm paraphrasing
what Dr. Anna Lembke has said,
and has written about
in her beautiful book,
"Dopamine Nation."
If you haven't read that
book, I highly recommend it.
Whether or not you have
issues with addiction
or you know people that do, or you don't,
it's an incredibly important read,
especially if you're
interested in understanding
motivated behaviors and ways
to channel your behaviors
in life toward healthy,
motivated behaviors,
and make sure that you avoid
some of the common pitfalls
that people fall into, not just addiction,
but things like overuse of social media
or wasting time in general,
it's a phenomenal book.
In that book, and of course,
within research articles,
you will find evidence of this so-called
pleasure pain balance that exists
within our dopamine circuits.
Nobody has dopamine
circuits that allow them
to escape this pleasure pain balance.
And the way this works is that anytime
that we engage in a behavior
or we ingest something
that increases our levels of dopamine,
there is a subsequent increase
in the neural circuits
that control our sense of
frustration, pain, and lack.
You can actually notice this phenomenon
if, for instance,
you're somebody who
really likes chocolate,
or you really like something else,
pay attention to the
way that you experience
indulging in that thing.
If you eat that piece of chocolate
and you really focus on
savoring its amazing taste,
you'll notice that it provides
some quenching of your desire
for let's say sweet stuff
or chocolate or both,
but right as you stop experiencing that,
right as that chocolate intake tapers off,
as you swallow it down your throat,
or you just pause for a second afterwards,
what you'll notice is
that your brain and body
actually orient toward wanting more.
And that wanting of more
is really the action
of the neural circuits that underlie pain
and are pushing your
dopamine levels back down.
And when these circuits
go awry or I should say,
when people fail to who control themselves
within the context of that
pleasure pain balance,
the typical behavior is to
reach for yet another chocolate
or to then look for something
that will quench that desire
and get dopamine levels back up.
Now the way these pleasure
pain circuits work
is very diabolical.
Because it turns out that were you to take
another piece of chocolate,
yes, your dopamine
levels would go back up,
but not to the same extent that they did
the first bite of chocolate that you had.
In fact, we can say that
the longer it's been
since you've indulged in
something that you really enjoy
or would like,
the greater the dopamine
you will experience
when you finally engage in that behavior
or indulge to that
thing, ingest that thing,
and the greater the dopamine increase,
the greater the subsequent
action of those pain circuits.
So this puts you on a
very complicated seesaw.
It's a very wobbly
precarious state to be in.
Which is not to say you shouldn't
have a piece of chocolate,
it's just to say that the
sweet taste of sweet things
in particular, things
that we crave very much
and we wait and wait and wait,
and then we allow ourselves to indulge.
Those trigger changes
in our neurochemistry,
in our neuro circuits,
that place us in a very vulnerable place,
to either want more and more of that thing
or to seek out other ways to
fill that kind of emptiness
that we feel or that gap,
like, oh, I would love more,
but I'm not going to allow myself more.
Now again, I'm not saying
that you shouldn't pursue
pleasurable things.
I mean this molecule
dopamine exists for a reason.
Frankly, because of its involvement
in sex and reproduction,
it's the reason we're all
here in the first place.
Because last time I checked,
the only way any of us got
here was one way or another,
sperm met egg and there was conception.
I still believe there are
no exceptions to that,
that I'm aware of anyways,
that is a process, or I should say,
the events leading up to that process
typically involve dopamine
in one way or another.
There are exceptions to that
too, but you get the idea.
These dopamine pathways are
not evil, they're not bad,
but once you understand the way they work,
you can leverage them to your advantage
as opposed to them leveraging
you to their advantage.
So when you ingest something sweet,
you perceive that sweet
taste and a cascade ensues
within your brain that makes you want more
of the sweet thing.
That's the conscious pathway
for sugar perception,
for sweet perception.
Now there's the second pathway,
the second pathway is what's called
the post-ingestive reinforcing
properties of sugar,
which is really just a fancy
nerd speak way of saying
there are events that
happen within your stomach
and below your conscious detection,
that are also driving you to
seek out sweet tasting things,
independent of their taste,
and foods that increase blood glucose,
independent of their taste.
In order to illustrate the immense power
of these subconscious
circuits for sugar seeking,
I'd like to describe an experiment.
And this is just one experiment of many,
of dozens or more experiments
done in animal models
and humans, which essentially
illustrate the same thing.
And as I describe this experiment,
I think you will come to understand
the power of these circuits.
I'll provide a link to
this study in the caption.
The first author is Freeman.
The paper was published in
Frontiers in Bioscience,
but there have been others,
papers in Nature Neuroscience,
papers in Neuron,
Cell Press journals, et cetera,
many, many journals, many, many papers.
If subjects are given the
choice of drinking plain water
or a sweet tasting fluid,
their preference for
the sweet tasting fluid
is much, much higher, right?
Sweet tastes better than plain water,
at least for most people
and certainly for animals.
Now, if, for instance,
you take an animal which
completely lacks sweet receptors,
and you can do this through
some molecular genetic tools
and gymnastics in the laboratory,
we call these knockout mice,
where you can knock out
a particular receptor
for sweet taste,
you can confirm that there's
no perception of sweet things
or at least no preference for sweet things
in those animals.
In humans, you can numb the mouth,
there are other pharmacologic ways
that you can eliminate sweet
receptors in the mouth.
And by doing that, you
people will tell you,
no, I can't taste anything sweet.
You could give them a ice cream,
you could give them pure sucrose,
you could give them table sugar,
and they wouldn't be able
to perceive it as sweet.
If you eliminate the perception
of sweet taste in the mouth
and you offer people
or laboratory animals,
water versus some sugar
containing solution,
you eliminate the preference
for the sugary solution.
Which tells us that
the perception of sweet
is important for the preference
for sweet tasting drink.
This is also true for sweet
tasting foods, I should mention.
However, in both animal
models and in humans,
after about 15 minutes,
subjects start preferring
the sugary water,
even though they can't
taste that it is sweeter.
So to repeat that,
if you eliminate the
ability to sense sweet,
to perceive sweetness in foods,
then you eliminate the preference
for sweet beverages or sweet foods.
So that's not surprising.
But if you wait about 15 minutes,
the preference for the sweet beverage
or the sweet food comes back.
Now that doesn't mean that they
can perceive the sweetness.
In fact, the way these experiments
are done is very clever.
You offer people various
cups of different things
or different food items.
And then you just look
at what they eat more of
or what they prefer to eat more of.
So this experiment is so crucial
because what it says
is that the preference
for sugar containing foods is in part
due to the sweetness of those foods,
but in part due to something else.
And this something else is what we call
the post-ingestive effect,
and as I mentioned before,
it took about 15 minutes.
And you've actually experienced this,
whether you realize it or not,
this phenomenon of post-ingestive
rewarding properties
of sweet foods,
meaning what happens in your body
when you ingest something that increases
your blood glucose very much,
has no doubt controlled
you from the inside,
below your awareness,
this was happening to you
and you didn't realize it.
And here's how it works.
We all have neurons within our gut.
These neurons have a name,
they're called neuropod cells.
Neuropod cells were famously discovered
by Professor, Dr. Diego
Bohorquez at Duke University.
And these cells respond
to, among other things,
to the presence of sugar within the gut.
So when we ingest a sugary food or drink,
or we ingest a food or
drink that simply contains
fructose, sucrose, glucose,
or some other form of sugar
that later, through metabolism,
will be converted into glucose,
the neuropod cells are able to register
the presence of those sweet
or glucose stimulating foods.
And in response to that,
send electrical signals,
because electrical signals are
the way neurons communicate,
up to the brain, via the
so-called vagus nerve.
The vagus nerve, of course,
being a nerve pathway,
famous for its role in relaxation.
That's kind of the assumption out there,
that it's always involved in relaxation,
that's not the case.
It's involved in a lot of
things besides relaxation.
But nonetheless,
these neuropod cells
send electrical signals
through a particular
highway within the vagus
to the so-called nodose
ganglion, and this is a cluster,
a ganglion is just a cluster of neurons.
And then the nodose ganglion
sends on information
to the nucleus of the solitary tract.
The nucleus of the solitary
tract is an area of the brain
that we're going to talk
about extensively today.
It's very important for
understanding sugar preference.
These neuropod cells
also trigger activation
of dopamine pathways within
the mesolimbic reward pathway.
In other words, there are
signals conveyed from the gut,
meaning stomach and
intestines, to the brain
anytime we ingest sweet foods,
but it has nothing to
do with our perception
of them being sweet, it has
everything to do with the fact
that sweetness of food is
almost always correlated
with an ability to increase blood glucose.
And the net effect of
this is a parallel pathway
by which dopamine is increased further.
Now, the experiment
that I described before
of animals or humans ingesting something
that contains sugar,
but not being able to
perceive its sweetness,
and yet, after a period of time,
still preferring that food or drink
to non-sugar containing food or drinks,
even though they can't
distinguish their taste,
is dependent on these neuropod
cells and related pathways.
What this may for you is that anytime
you eat something sweet,
that substance is
actually causing your gut,
your stomach and your intestine,
or to be more precise,
I should say, that
substance, food substance,
is causing the neuropod cells
in your stomach and intestines
to send a parallel set of
signals up to your brain saying,
eat more of that, or simply
eat more, eat more, eat more,
and preferably eat more sweet foods.
So we've all heard of hidden sugars,
meaning the sugars that
manufacturers have put into foods
and disguised them with other flavors.
I talked about this in
the episode on salt,
using salt to mask the taste of sweetness
so that people ingest more sugar.
That is not an accident
that hidden sugars are
often hidden with salt
or with other flavors.
It's done so that people
will, meaning you or me,
will want to ingest more
of a particular food,
independent of how sweet that food tastes.
And in fact, some crackers, for instance,
chips for instance, you might
think, oh, well, you know,
chips, they're not sweet,
they're salty and savory.
And again, I'll mention, I
love salty and savory foods,
including certain foods, I love
kettle chips, for instance,
I try not to walk by them
in the grocery store.
I usually have to eat one
bag while I'm in the store,
and then another later.
The savory foods are often
laden with these hidden sugars
that we can't register as sweetness,
but trigger the neuropod cells,
which then further trigger dopamine,
which make us want more of them.
Now we may be able to
resist eating more of them,
but it makes us crave
more food in general.
Now we will talk about ways
to regulate this pathway,
to sort of intervene in
this subconscious pathway.
But for now I'm hoping
that just the understanding
that we all have this pathway,
this is hardwired into our body,
could potentially allow
people to better understand
why is it that their
cravings are so intense,
that it's not necessarily just
about the taste of that food.
And when you consider this
in concert with the fact
that we have this dopamine pain
pleasure balance, excuse me,
that I referred to earlier,
you start to realize that
there are multiple mechanisms
hardwired into us, that make
it especially hard to not eat
the sweet thing or to not eat
the food that we're craving.
And indeed, that's the case.
We have two major accelerators.
It's like a car with two accelerators,
and we will talk about the brakes,
but two ways that really
get us into forward motion
toward pursuing the
consumption of sweet foods.
Now, if it doesn't already
seem diabolical enough,
that sweet things that
we perceive as sweet,
make us want to eat more of those
because of dopamine and then send us down
this pain pleasure pathway
that I mentioned earlier,
and the fact that we have
this subconscious circuit
coming from the neuropod cells in our gut
that are registering the presence of sugar
or glucose increasing foods in our gut
and sending those signals to
the brain for yet more dopamine
and pain pleasure challenges,
there's a third layer to this whole thing.
And that has to do with how sugar
is metabolized in the brain.
Or I should say how glucose is used.
Without getting into too much detail,
some of the more beautiful
studies of neuroimaging
and evaluating which
brain areas are active
when we eat certain foods
were done by Dr. Dana Small's
lab at Yale University,
and in some of her previous
work when she was elsewhere,
and of course by other laboratories too.
And they used an approach called
positron emission tomography,
and they and others have used
PET scanning as it's called,
positron mission tomography,
along with an tool
called 2-Deoxy-D-glucose.
2-Deoxy-D-glucose is actually
involved in the procedure
of seeing which brain areas are active
when people eat foods or engage
in other types of behaviors.
But the way that 2-Deoxy-D-glucose,
sometimes shortened 2DG.
The way that it works is
to block glucose uptake
from neurons.
And instead, bring along with it,
a marker that one can see through imaging.
So in other words,
a tool for looking at what
parts of the brain are active
when eating particular foods,
actually prevents foods such as sugar,
from allowing glucose to
get into particular neurons.
Now that might seem like a bad situation,
you'd say, well, wait,
you're trying to understand
how sugar works in the brain,
and then you block the
ability for sugar, glucose,
to bind to, or be used by these neurons,
because of the thing that
you're using for the experiment.
Exactly, it's a huge problem,
but it turns out to be a huge problem
that led to a great insight.
And the great insight is this,
the preference for sweet
tasting foods and liquids
is actually blocked by 2-Deoxy-D-glucose.
What that means, experimentally,
but also in terms of what
it means for you and me
in the real world, is that there's yet
a third parallel pathway
that's related to the use of blood sugar,
the use of glucose by neurons,
that further reinforces our
desire to eat more sweet things.
And the preference for sweet foods
can actually be eliminated
through 2-Deoxy-D-glucose.
Now I am definitely don't
want people going out
and consuming 2-Deoxy-D-glucose.
This is a laboratory tool,
it is not something that
you should be ingesting.
So don't go look it up
and try and get some,
there might be other uses for
it, but that's not the point.
The point is that it is the
sweet taste of sugary foods.
It is the signals coming from your gut,
from your digestive tract to your brain,
and it's the use of the
metabolic consequences
of sugary foods that are
acting as a three pronged push
on your desire to consume
more sugary foods.
So this car analogy that I used before,
where it's some weird car
that has two accelerators,
it actually has three accelerators.
And so with three accelerators,
all pushing the system hard,
we can say, wow,
there must be something really
special about this pathway.
And indeed there is,
this pathway is the quickest
source of fuel for the brain
and the rest of the nervous system,
it's the source of fuel for
the brain and nervous system.
And I realize, as I say
that all the ketonistas
are probably going no,
actually ketones are the preferred source.
Okay, i acknowledge that
there are conditions
under which you can bring
your blood glucose very low,
and there are reasons to do that.
Actually ketosis has been a
terrifically successful treatment
for a lot of forms of epilepsy,
in particular, pediatric epilepsy.
Many people do derive
benefit from ketogenic diets,
so I'm not knocking ketogenic diets,
but if you were to look at
what neurons normally prefer,
meaning in a typical diet
regimen, it would be glucose.
And the fact that fructose
is eventually converted to glucose,
the fact that when we ingest sucrose,
it's eventually converted into
a fuel that neurons can use,
that's very much in the glucose pathway,
what you basically arrive at is the fact
that your nervous system is
a glucose consuming machine.
And you've got at least three pathways,
of which I've described,
that are pushing on your brain consciously
and subconsciously to get
you to seek and consume
more sugar.
Now that all sounds like a
pretty depressing picture,
at least for those of you
that are trying to reduce
your sugar intake.
And of course we can
all reduce sugar intake
by way of sheer will,
we can not have those foods at home,
we can restrict ourselves from those.
But there are some things that we all can
and perhaps should do in order
to regulate these pathways
such that we don't feel
so controlled by them,
but rather that we control their output.
And of course they are us and we are them,
so this gets into all sorts
of issues of consciousness
and freewill that I
certainly don't want to cover
in this episode.
But nonetheless, I think
once you understand
that these circuits exist
and you understand that there
are simple substitutions
and modifications that one
can make to their food intake
that can work within these pathways
and even bypass some of these pathways,
you start to realize that
you have a lot more control
over sugar intake and sugar appetite
than you previously thought.
Now, many of you have heard of
the so-called glycemic index.
The glycemic index is a measure of
how quickly blood sugar rises
after ingesting particular foods.
And very broadly speaking,
we can say that there are
low glycemic index foods,
of less than 55, typically,
is the measurement,
or medium glycemic index foods,
which go from about 55 to 69,
and then so called high glycemic
foods, which are above 70.
And of course there's additional nuance
related to glycemic load
and many more features
of the glycemic index.
A couple of things to understand
about how the glycemic index is measured.
And then I'd like to
just briefly talk about
how the glycemic index can
be leveraged to short circuit
some of the neural circuits
that would otherwise lead us
to crave and perhaps
even ingest sugar foods.
First of all, measurements
of glycemic indices of food
are typically made by having
people ingest those foods
in isolation.
And in general, we can say
that anytime we ingest fiber
and/or fat, lipids, along
with a particular food,
it will reduce the glycemic
index of that particular food,
either the absolute level of blood glucose
that a particular food causes
or the rate at which that
elevation in blood glucose occurs.
And this is why there are some
seemingly paradoxical aspects
to sweet stuff in terms
of the glycemic index.
For instance, Ice cream
has a lower glycemic index,
provided its ice cream that includes fat,
which I hope it would,
'cause that's the good tasting ice cream,
in my opinion,
compared to something like
mangoes or table sugar, right?
So the glycemic index is
not something to hold holy,
in most cases,
because most people are not
ingesting foods in isolation.
And there's actually a lot of argument
as to whether or not the glycemic index
is really as vital as some people claim.
There's also the context
in which you ingest particular foods.
As I mentioned earlier,
after I do hard training of any kind,
meaning training that
ought to deplete glycogen,
so hard resistance training,
I actually make it a point to ingest
some very sweet high
glycemic foods like a mango,
I'll also ingest some starches
'cause I'm trying to replenish glycogen.
I'm also trying to spike
my blood sugar a little bit
because that can be advantageous
in terms of certain strength
and hypertrophy protocols,
et cetera.
But most of the time I'm avoiding
these high glycemic foods
and high sugar foods, I
should point that out.
Now, why am I telling you
about the glycemic index?
Well, if we zoom out
and take our perspective
on all of this discussion
about the glycemic index,
through the lens of the nervous system,
and we remind ourselves that neurons
prefer glucose for energy
and that all sweet things,
or things that we perceive as sweet,
but also sweet things that
are ingested and registered
by those neuropod cells in our gut
trigger the release of dopamine
and trigger these neural circuits
to make us want to eat
more of these foods,
what we start to realize
is that a sharp rise
in blood glucose or a very
high degree of elevation
in blood glucose,
is going to be a much more potent signal
than would a more moderate
rise in blood glucose
or a slower rise in blood glucose.
So if we think about the
analogy of three accelerators,
meaning three parallel neural circuits,
all essentially there
to get us to seek out
and consume more sweet
tasting and sugary foods,
well then the glycemic index
is sort of our measurement
of how hard we are pushing down
or how fast we are pushing down
on those three accelerators.
And so for those of you that are trying to
reduce sugar take,
and you want to do that
through an understanding
of how these neural circuits work,
and you want to short circuit
some of the dopamine release
that's caused by ingesting sugary foods.
It can be advantageous
to ingest sweet foods,
either alone or in combination with foods
that reduce glycemic index
or reduce glycemic load.
So that might mean making
different food choices.
So paying attention to sweet tasting foods
that can satisfy sugar cravings,
but do not have as steep or I should say,
do not cause as steep
a rise in blood sugar,
or it could mean consuming other foods
along with sweet foods
in order to reduce the glycemic index
and thereby, slow or blunt
the release of dopamine.
You might think, well, why
would I want to do that?
I want the maximum dopamine output
in response to a given sweet food.
I don't just want the you know, level 10.
I want the level 100 output of dopamine.
But you really don't,
because of the pleasure pain
balance that dopamine causes.
And in fact, if we consider
some of the non-food substances
that really push hard on
these dopamine pathways,
we can come up with a somewhat sinister,
but nonetheless appropriate analogy.
The drug, cocaine, causes
very robust, potent increases
in dopamine within the brain,
and typically causes people
to want to ingest more cocaine
because of those sharp
increases in dopamine.
But within the category
of the drug cocaine,
there are various modes of ingestion.
Some people inhale it,
some people will inject it intravenously,
some people will smoke it,
and those different
forms of taking cocaine
actually impact the dopamine
circuits differently.
And it turns out that crack cocaine,
the smokable form of cocaine rock,
increases dopamine to a very high degree,
but also very quickly.
And it is the sharp rise
in dopamine over time,
not so much the absolute
level of dopamine,
that makes crack cocaine
so absolutely addictive.
So sometimes you'll hear, you know,
sugar is like crack,
well, and that's getting a little extreme
because even though I don't
think the measurements
have been done in the same experiment,
I think it's reasonable to think
that the absolute level of dopamine caused
by ingesting sugar, at
least for most people,
is not going to be as high as
the absolute level of dopamine
caused by smoking crack.
Of course it goes without saying,
please don't do cocaine
in any form, by the way.
It is appropriate to say that
the rate of dopamine increase
over time has a profound
effect on how people will,
and if people will,
go on to want to pursue
more of what caused
that increase in dopamine.
So what I'm basically saying
is if you're going to ingest
sweet foods in order to
satisfy a sweet craving,
ingesting sweet foods for which
the glycemic index is lower
or in which you've adjusted
those glycemic index foods
through the co-ingestion
of fiber, or maybe fat,
might be beneficial.
So is this justification
for putting peanut butter
on that piece of chocolate
or for having a of ice
cream along with the mango
that you're craving?
In some sense, yes, however,
there's also the issue of
how sweet and how delicious
something tastes.
Highly palatable foods,
absolutely delicious foods,
trigger that one neural circuit,
that one accelerator that
we were talking about
in terms of our analogy
of three accelerators,
and the more delicious something
tastes within our mouth,
the further increase in dopamine.
So if you really wanted to
adjust your sugar cravings
and you really still want
to ingest some sugary foods,
you probably would better
off combining fiber
with that sugary or sweet food.
Now I do realize that
it's somewhat unusual
and you probably get some strange stares,
if you decided to consume broccoli,
for instance, along with your chocolate,
or with a another dessert
that would otherwise
cause a steep increase in blood sugar
and has a high glycemic index.
But nonetheless, if your goal is to blunt
your sugar cravings,
what you really need to do is
blunt that dopamine increase.
So what we're really talking about here
is trying to reduce the dopamine signal
that is the consequence
of ingesting sweet foods.
And we're talking about doing that
through these different parallel pathways,
not just by preventing sweet taste,
but also by preventing
the post-ingestive effects
of sweet foods.
And of course the backdrop to all of this
is that most of us, again,
most of us, not all of us,
should probably be ingesting
fewer refined sugars.
Certainly there are exceptions to that.
But I think the bulk of
data point to the fact
that ingesting these highly palatable,
certainly highly palatable,
highly processed foods,
or foods that contain a lot
of high fructose corn syrup,
can be really deleterious to our health,
especially in kids.
And I'm not going to cite
off a bunch of statistics,
you've all heard them before,
that you know, for hundreds of
years, we ingested, you know,
the equivalent of a few cups
or pounds of sugar per year.
And you know, now people are ingesting
hundreds of pounds of sugar per year.
The major culprit always
seems to be sugary drinks,
meaning soft drinks, and I
think indeed that's the case.
I do want to point out the incredible work
of Dr. Robert Lustig,
who's a pediatric endocrinologist
at the University of
California San Francisco,
who was really early in the
game of voicing the dangers
of so-called hidden sugars
and highly processed foods,
there are other people, of
course, now talking about this.
His laboratory has done important
work showing for instance,
that if high fructose corn syrup
or even just fructose is
replaced with glucose,
even if the same number
calories is ingested,
that there are important
meaning significant reductions
in type two diabetes,
some of the metabolic syndromes
associated with high fructose corn syrup
and on and on and on.
And of course there are other
culprits in type two diabetes,
there are other factors that
are going to lead to obesity.
But I think that work
from Lustig and others
has really illustrated that
we should all be trying
to reduce our intake of
highly refined sugars
and high fructose corn syrup.
And certainly trying to reduce our intake
of very sugary drinks,
not just soft drinks,
but also fruit juices that
contain a lot of sugar.
Now, even for people that
are of healthy weight
and who don't have metabolic syndromes,
there may be an additional reason
to not want to ingest very sweet foods
and highly refined sugars.
And this has to do with
a new and emerging area
of nutrition neuroscience.
And I want to point out that
these are new data, right,
so it's not a lock,
the double blind placebo
controlled studies
in large populations
have not been finished.
So I want to make sure that that's clear,
but I also want to make clear
what some of the really exciting data,
coming from Dana Small's lab at Yale,
and from other laboratories are showing.
And this has to do with what's called
conditioned taste preference.
Using a kind of Pavlovian
paradigm, what they do,
is they have people, and these
studies were done in people,
ingest maltodextrin, which
increases blood glucose,
doesn't have much flavor,
but even if it does have a
little bit of subtle flavor,
the maltodextrin is cloaked
by some other flavor.
And by cloaking it with that other flavor
or pairing it with that other flavor,
what they find is that over time,
because the maltodextrin
increases blood glucose,
and they're ingesting a particular flavor
along with that maltodextrin,
they can then remove the maltodextrin,
and the flavor will induce
an increase in insulin.
The increase in insulin of course,
is the consequence of
the fact that anytime
there's a rise in blood glucose,
provided the person isn't diabetic,
there's a parallel increase in insulin.
Now this is very interesting
because what it says is,
well at a first pass, it says
that we are very Pavlovian
in terms of our physiological
responses to foods
and particular flavors
come to be associated
with particular patterns
of blood glucose increase
and hence patterns of insulin increase,
because of course,
insulin manages glucose in the bloodstream
as I mentioned earlier.
This also has implications
for understanding
things like artificial sweeteners.
And here I want to
highlight that this is still
very controversial work, needs
more data, but nonetheless,
I'd like to share it with
you for consideration.
The small laboratory has
done studies in humans,
both in adults and in children,
showing that if the flavor
of artificial sweeteners
is paired with maltodextrin,
and then the maltodextrin is removed,
that the artificial sweetener taste itself
can subsequently increase
insulin in the bloodstream.
In other words, taking something
that increases blood sugar,
attaching a flavor experience to that,
having children or
adults ingest that thing,
allows the nervous system
to associate that flavor
with that increase in blood glucose.
But then you can remove the
glucose increasing substance,
and the flavor alone will increase insulin
because insulin typically
follows blood glucose.
So this is a conditioning effect.
Now, the reason these
data are controversial
is several fold.
First of all, the landscape
around the discussion
around artificial sweeteners
is definitely what I would call
a barbed wire topic.
And I want to preface what I'm
about to say next by saying,
I actually ingest artificial sweeteners.
I will have the occasional
diet soda, not every day,
maybe I don't know, once or twice a month.
I don't particularly like the taste,
but I'll do it just 'cause it's around,
and I want some caffeine
and I like the carbonation
if I'm on a plane or something,
I do ingest plant-based
non-caloric sweeteners.
To my knowledge, there have
not been high quality studies
of plant-based non-caloric sweeteners
in the context that I'm referring to here.
Nonetheless, these studies
show that particular flavors
can be conditioned to
cause an insulin increase.
And the flavor associated with
certain artificial sweeteners
is included in that category of flavors
that can induce insulin,
even in the absence of something
that can increase blood glucose.
Now the simple takeaway from these studies
would be the following,
and this is actually one
interpretation that Dana Small
has offered to her data,
but she offers other
interpretations as well.
One of interpretation is that if people
are going to ingest artificial sweeteners,
and they do that along with foods
that very sharply increase blood glucose,
then there is the potential,
I highlight the potential,
for those same artificial
sweeteners to increase insulin,
even in the absence of food.
In other words, let's
just draw the scenario out
in the real world.
You're having a diet soda
along with a cheeseburger and fries.
You do that every day for lunch, okay?
Somewhat extreme example,
but natural world example,
you do that every day for lunch.
And then you just have a diet soda alone.
The extreme interpretation of the data
that they've collected says,
well, that diet soda alone
will increase insulin,
even though there's no
increase in blood glucose
because you haven't ingested food with it
because you conditioned that
taste of artificial sweetener
to the experience of a rise
in glucose and hence insulin.
Now the counter argument to this would be,
well, that's a very unusual situation,
maltodextrin causes big
increases in blood glucose,
so that's not really a fair experiment
or it's not a natural world experiment.
And I think that's a decent assessment.
Although I will point out
that one of the reasons
why this study is so controversial
or why these data are so controversial,
is that the experiment
actually had to be stopped.
And particularly the
experiment in children
had to be stopped because
the changes in insulin
that were observed early in
the study were so detrimental,
that the institutional review
board, quite appropriately,
said, we can't do this to these kids.
They're experiencing these
odd shifts in insulin
that are not healthy for them
when they're just ingesting
artificial sweeteners
in the absence of these
glucose increasing foods.
So once again, I do ingest
artificial sweeteners,
I'm not saying that they are dangerous,
I'm not saying that
they are not dangerous,
I'm saying that you have
to decide for yourself.
In previous episodes,
I've highlighted that
artificial sweeteners
have been shown in studies of animals,
that when given in very high
doses, sucralose in particular,
there can be fairly robust
disruption to the gut microbiome,
which is vital for immune
health and brain health,
et cetera, et cetera.
But thus far, our knowledge
of how artificial sweeteners
negatively impacts or positively
impacts, I should say,
the microbiome and other
deleterious effects on the body,
has mainly been explored
in animal studies.
Again, the work by Dana Small
has been done in humans.
There's some parallel work
by others in animal models.
I bring it up today to
illustrate the following point.
Normally we have a pathway
that we don't have to condition at all,
it's there from birth,
whereby ingestion of sweet foods
causes increases in dopamine.
And there are parallel pathways
by which neurons in our gut
and elsewhere in our body,
trigger further increases in dopamine.
There's no need for a conditioned response
or to become Pavlovian about this, right?
You're hardwired to want
to eat sweet things,
by at least two and probably
three parallel pathways.
Now the work from Dana
Small's lab and others
that have illustrated this
conditioned flavor preference,
I think beautifully show that any flavor
that's associated with a glucose spike
or a long sustained increase in glucose
can also be conditioned.
In other words, the circuits for dopamine
that reinforce the desire
to eat particular things
is not unique to the sugar pathway.
And this is one of the reasons I believe,
why ingestion of sweet foods
doesn't just us to want
to eat more sweet foods,
I think that is absolutely clear
based on animal data and on human data,
I think that's robust,
it's actually the stuff of textbooks now,
but in addition, ingesting sweet foods
and/or foods that raise blood glucose,
but that we don't perceive as sweet.
So for instance, foods with hidden sugars,
sugars that have been masked
asked by salty or spicy taste,
increases our desire for
glucose elevating foods
and food, generally,
I think that's the only
logical interpretation
of the data that I can arrive at.
So for people that struggle
with regulating their appetite
or with regulating their sugar appetite,
I think the understanding of
conditioned flavor preference,
while a little bit complicated,
ought to be useful in
trying to navigate reducing
sugar cravings and sugar intake.
As a segue into tools
to control sugar intake,
as a means to both regulate
sugar intake itself,
as well as food intake overall
and steer us towards healthier choices.
I'd like to talk about some
of the special populations
out there that might want
to be especially wary
of having a dysregulated
sugar appetite system.
And the group I'm
referring to specifically
are those with attention
deficit hyperactivity disorder
or, I should say, and/or,
people who have issues with
focus and attention, generally.
And I think more and more nowadays,
I'm hearing that people are
having a hard time focusing.
This probably has something
to do with our interactions
with electronic devices.
As I always say, if a picture
is worth a thousand words,
a movie is worth a million pictures,
and the fact that we
can access so any movies
just by scrolling with our thumb,
is something that the nervous system
has just never contended
with before in human history.
I'm confident in that.
And it's not that it can't deal with it,
the question is what's the trade off?
What are the consequences of that?
So attention and ability
to focus is obviously key
to success in school,
success in relationships,
success in the workplace,
and success in life.
We could probably even go so
far as to say one's ability
to succeed in anything is
proportional to one's ability
to focus and then deliberately defocus
when the time comes to defocus, right?
'Cause we all need rest
and we need to disengage
and then reengage,
If you look at the sum
total of the meta-analysis
and the clinical data
on ADHD and nutrition,
you arrive at a pretty clear answer,
which is that sugar consumption,
in particular, highly refined sugars,
is just not good for people with ADHD
or with attentional issues.
Now, as I say that, I
also want you to recall
the earlier study that I referred to,
whereby the tuning of neurons in the brain
is highly dependent on glucose.
So this doesn't mean consuming no glucose
is going to be a good idea.
It doesn't mean that the ketogenic diet
is necessarily the best diet for ADHD.
Although there are some
people pursuing that
and exploring that, and we'll
do yet another episode on ADHD
at some point that go was a
little bit deeper into that,
because there's some new data.
I did do a very long and fairly
extensive episode on ADHD.
You're welcome to look that
up if you like in our archive,
excuse me, in our archive
at hubermanlab.com,
it's all timestamped.
So, you know, because the
number of people said,
oh, you know, it's an episode on ADHD
and you made it two and a half hours long.
Yes we did, because we wanted
it to be as comprehensive
as we could at the time.
But it is timestamped,
you can just jump to the
particular topics of interest
and there's short little cassettes there.
Now, if you'd like to
know upon what I'm basing
this statement that sugar consumption
and highly refined sugar consumption
is potentially bad for ADHD,
I'm basing this mainly on the conclusions
of a really nice paper,
the title of the paper is
"Sugar Consumption, Sugar
Sweetened Beverages,
and Attention Deficit
Hyperactivity Disorder:
A Systematic Review and Meta-Analysis."
And this is a paper,
we'll put a link to this in the caption.
This was published in
Complementary Therapies in Medicine
which is a bit of an atypical
journal in some sense.
But I really like this meta-analysis.
The sum total of this
meta-analysis is really that when,
especially kids, get beyond
four sugary drinks per week,
so four sodas of a typical 12 ounce soda,
when they get past four
12 ounce sugary sodas,
they didn't, as far as I know,
look at artificially sweetened sodas.
That's when you start
to see a shift towards
more negative outcomes, more
symptoms of existing ADHD.
Now where the controversy comes in
is whether or not sugar consumption
can actually trigger or cause ADHD.
And I don't think we can conclude
that at all at this time.
And this review, if you
decide to check it out,
review/meta-analysis, I should say,
if you decide to check it out,
goes into some of the nuance around that.
What's also interesting in
terms of ADHD and sugar intake,
and it probably has
relevance to all of us,
is that they also cover
some of the interesting data
showing that supplementation
with omega-3 fatty acids
can actually beneficial for people,
in particular kids with ADHD,
I've talked before about
the utility of omega-3s,
that's been shown in various studies
that have compared
omega-3 fatty acid intake
to say prescription
antidepressants, like SSRIs,
like Prozac, Zoloft,
and similar, Fluoxetine,
and the results of those
studies are pretty clear,
at least to me,
that provided that one gets
at least one gram of EPA,
essential fatty acids,
so it's not just getting one gram per day,
but one or more grams
per day of the EPA form
of essential fatty acid,
can rival some prescription
antidepressants
and/or decrease the
amount of antidepressants
that's required to take.
Which for a lot of people
can be a very useful thing
because of the side effect profile
of many of those antidepressants.
Of course, talk to your
psychiatrist, talk to your doctor,
but the omega-3s are no doubt powerful.
And then of course there's a whole story
about omega-3s and heart health.
And of course, like anything else,
there's some controversy around omega-3s,
but I think the data
are clear enough to me
around mood and cardiovascular health,
that certainly I personally ingest them.
But as always, I always say,
anytime you're going to
add or remove anything
from your nutrition,
supplementation, exercise,
or otherwise your lifestyle,
definitely consult with a
board certified physician.
I don't just say that to protect me,
I say that to protect you,
you are responsible for
your health ultimately.
So omega-3 supplementation
has been shown to be
beneficial for ADHD.
Why am I talking about this in the context
of an episode on sugar
and the nervous system?
Well, if you remember
those neuropod cells,
those cells in your gut
that respond to sugar
and send signals up to the brain
to cause the release of dopamine.
Well, it turns out that
neuropod cells also respond to
amino acids and to fatty acids,
in particular, essential fatty acids.
So these cells that we
call neuropod cells,
have three jobs.
One is to levels of sugar in the gut,
the other is to detect
levels of amino acids,
and to detect levels of
particular essential fatty acids,
and communicate that
information to the brain.
And I should point out
when I say communicate
that information, they're
not actually saying,
hey, there's amino acids here,
or hey, there's sugar here,
or, hey, there's essential fatty acids,
because the language of these
cells is somewhat generic.
It's just the firing of
electrical potentials.
But that's the key point,
it's generic and all three
or any of those three,
sugar, essential fatty
acids, or amino acids,
will trigger these neurons to signal
to the brain to increase dopamine.
And it is not coincidental
that omega-3 fatty acid
supplementation can help ameliorate
some of the symptoms of ADHD
by way of presumably increasing dopamine
in this neuropod to dopamine pathway
that we talked about earlier.
The whole thing has a very
nice logical structure to it.
And points to yet again,
the immense value of
bringing the proper amounts,
maybe even supplementing
the proper amounts
of omega-3 fatty acids and the
proper amounts of amino acids
into the gut as a way to supplant
some of the stimulation of these pathways
that would otherwise be caused by sugar.
There's actually a version
of this where one could say,
if you want to reduce sugar cravings,
you might consider
increasing certain forms
of amino acid intake or certain
forms of fatty acid intake.
So what are some ways that we
can reduce our sugar cravings,
and ideally ways that we can do that,
that also benefit us in other ways,
both nutritionally and from
the neuroscience standpoint?
Well, these neuropod cells that respond to
and signal the brain when we
ingest sugar, as I mentioned,
also respond to amino acids
and essential fatty acids.
We already talked about
the essential fatty acids.
I make it a particular
point to ingest anywhere
from one to three grams, that's grams,
of EPA essential fatty acid per day.
I make it a point to do
that with the ingestion
of high quality omega-3s.
For me, the simplest way to do that,
and I think for most people,
the lowest cost way to do that,
is to use some liquid form of fish oil
or some capsule form of fish oil.
You really do have to see
how much essential fatty acid
in the form of EPA is in those.
If you try and do that
only through capsules,
it can get kind of expensive,
depending on which
particular brands you use,
some have more EPA, some less.
You can, of course also
do this through foods,
you can do this with non fish sources,
through things like algae,
and there's some other forms,
you can look it up online now,
plant-based sources of EPAs,
you can do this with
high quality fish oil.
In any case, that does
seem at least based on
a modest amount, but
nonetheless solid literature,
to reduce sugar cravings somewhat,
but that could easily be by
mere replacement of calories.
So we don't know yet
based on human studies,
whether or not the ingestion of those EPAs
is specifically activating
the neuropod cells,
which specifically
activates dopamine release
and bypasses the need for,
or the craving for sugar.
We don't know that yet.
But logically, it holds up to assume that.
The fact that these neuropod cells
and I should say other
neurons within the gut
respond very robustly to the presence
of particular amino acids
is also a potential lever
by which one could reduce sugar cravings.
And there's an interesting literature
around the amino acid, glutamine,
in particular supplementing
with the amino acid, glutamine,
as it relates to sugar cravings,
and certainly as it relates
to other aspects of the gut,
in particular leaky gut.
The use of supplemental glutamine
to try and treat leaky gut
is not a new phenomenon.
There are other approaches too, of course.
But there are many people
who are experimenting
with supplementing with
glutamine, several grams per day,
often even, you know, five
grams distributed through
three or four different
servings throughout the day
as a way to blunt their sugar cravings.
Now there has not yet been
a large scale clinical trial
using glutamine to reduce sugar cravings,
but the results of the few
studies that I looked at,
as well as my understanding of the logic
of these neuro circuits,
including the neuropod cells,
brings us to a conclusion
that it makes sense
why if there's a population
of neurons within our gut,
that responds very robustly
to the presence of sugar,
fatty acids, or amino acids,
that the intake of particular amino acids
would allow the dopamine pathways
that might otherwise be triggered by sugar
to be triggered by
something like glutamine,
which has very few or no calories.
And in fact, having talked
about this previously,
a number of people that I
know went out and tried this,
now this is of course is
what I call anec data, right?
This is not a quality peer reviewed study,
this is anec data.
Many of them have reported back
that they actually feel
as if their sugar cravings
are reduced.
I know some people who
actually take glutamine
and mix it with full fat cream
and take it kind of like
a shot of full fat cream,
which sounds absolutely
delicious by the way,
glutamine is a little bit chalky,
so it's not that great
tasting to ingest with sugar.
I should mention, if you do
try and take this approach
of ingesting glutamine
to reduce sugar cravings,
you want to increase
the amount of glutamine
that you take somewhat gradually.
It can create some gastric distress
if you just, you know,
I certainly wouldn't take
a big table spoon of it,
throw it in water and chug
it down three times a day.
Some of you with very hardy stomachs
can probably tolerate that.
You know, if you're like my bulldog,
which unfortunately
passed away, but Costello,
I always imagine that if ever
we did an autopsy on him,
he'd have like a license plate
and like a human being in his gut,
'cause it seemed like
he could ingest anything
with no issues,
but of course, many people
have kind of sensitive guts.
So if you're going to try taking glutamine
as a means to reduce sugar cravings,
just know that the
studies are still ongoing.
Some people have achieved benefit.
Please also realize that
there's an entire literature
devoted to the potential
hazards of increasing glutamine
if you have a preexisting cancer.
So if you have cancer
or you're cancer prone,
I would really discourage
you from this approach.
And in any case, as always,
talk to your doctor.
The logic nonetheless is there,
why increasing amino acid
intake or fatty acid intake
might decrease sugar craving.
Now there are other ways
to reduce sugar craving
and there are certainly
ways to reduce the sharp
rise in blood glucose that can occur
when we ingest sugary sweet foods
or even just an abundance
of carbohydrate foods,
and there are a huge
number of these things.
I'm going to sort of
layer up through the ones
that you might find in your
cupboard, at the grocery store,
and then get into some
of the more extravagant
or I should say, esoteric ones,
many of which however can be quite potent.
The first of which is
simple lemon juice, right,
or lime juice.
There was an old lore
and actually some papers,
pointing to the idea that
the ingestion of vinegar,
either white vinegar or wine vinegar,
could somehow blunt blood glucose
after the ingestion of sugary foods
or the ingestion of a lot
of carbohydrate foods,
or even just a big meal.
Actually, Tim Ferris, I should
say the great Tim Ferris,
'cause I do have great
respect for the fact
that he seems to be about 10
years ahead of everything,
both in terms of nutrition
and skill learning
and things of that sort,
many of the things that
he predicted in his books,
"The Four Hour Body"
and "The Four Hour Chef"
actually turned out to be
true based on scientific data,
some of which only exists
in the animal models,
but now also some predictions
that played out to be true
in both the animal models
and and the human models.
So I think that Tim
certainly deserves a hat tip
for the fact that he
experimented with these methods
and reported his experiences
with those methods
and that now some of them, many of them,
have been validated by
what I perceive to be
quality science.
He talked about the fact that,
at least in his experiments on himself,
the ingestion of vinegar
did not seem to blunt
blood glucose, and he was using
continuous glucose monitors.
These incidentally, another
example of where Ferris
was early to the game and the rest of us
are kind of just in his wake.
He talked about the use
of blood glucose monitors,
those, I think at the time
were implanted below the skin.
Nowadays there are less
invasive blood glucose monitors,
things like Levels and so forth,
and these are actually
becoming pretty popular.
I've worn one of these before.
They're actually pretty informative.
I learned for instance,
that when I go in the sauna
that I experience a sharp
rise in blood glucose.
And that makes sense because
of the dehydration associated
with being in the sauna,
a lot of sweating,
the concentration of sugar
in the bloodstream goes up.
So there's some other
things that certain foods
affect my blood glucose
one way or another.
It's kind of an interesting
and fun experiment
that some of you might be
interested in doing as well.
Regardless, there are now
data pointing to the fact
that lemon juice and lime juice,
a couple tablespoons or so,
if ingested before, or
even during, or even after,
consumption of sugary foods,
or I should say foods that
sharply increase blood glucose
or large carbohydrate meals,
can actually blunt the
blood glucose response.
And I did see that when I did
my own experiments on myself
with a continuous glucose monitor,
it was kind of fun to
do those experiments.
I preferred to do those experiments
by eating somewhat larger meals
of things that didn't
contain a lot of sugar.
I saw some big increases in blood glucose
in certain instances,
and then I would ingest some
lemon juice or lime juice,
typically mixed in with water.
And sure enough, you could see a blunting
of the blood glucose response.
And of course this was
real time, continuous,
hence continuous, blood
glucose monitoring.
So for those of you that are interested
in blunting your blood sugar
response, certain foods,
that's a simple, low cost way to do that,
if you want to explore it.
I will say, if you are fasting
and you already have low blood glucose,
and you ingest lemon juice,
or I should say some lemon juice and water
or lime juice and water,
be careful because you can
actually become hypoglycemic.
For the very same reasons
that that lemon juice
and lime juice can blunt blood glucose
when your blood glucose
levels are moderate to high,
you can also reduce blood
glucose levels even further
when blood glucose levels are low.
Now that's lemon juice
and lime juice there.
But we can't say that has
to do with acidic things,
generally.
And just as a side point,
many of you have probably
seen in the store,
so called adjusted pH
waters or foods and drinks
that are supposed to adjust your pH.
Hate to break it to you,
but your pH is very tightly regulated
throughout your brain and body.
You do not want this to change.
It is entirely impossible,
at least in any safe way,
that you would become
quote unquote more alkaline
by ingesting an alkaline
water or something like that.
It is true that the pH,
your alkalinity and acidity
varies in different
compartments in your body,
that's important.
Unless you are hemorrhaging or vomiting,
or there's something badly
wrong with you, health wise,
and you're in a really dire circumstance,
you don't want big shifts in your body pH
and your body has all sorts
of ways of buffering against
changes in pH.
So I encourage you not to fall on the,
or hop on the bandwagon of adjusting pH
and becoming less acidic,
and that kind of thing.
When you ingest lemon juice or lime juice,
the mechanism by which
it blunts blood glucose
is probably twofold.
One is probably through
the post-ingestive effects
of glucose in the gut,
meaning the way in which
sugars are interacting
with neurons and other
components of your gut circuitry
to impact things like
gastric emptying time,
to impact things like the
firing of those neuropod cells
and their signaling to the brain.
But almost certainly it
has something to do also
with the perception of
sour taste on the tongue.
We didn't go into this too
much today, but you, of course,
don't just have sweet taste
receptors in your mouth,
you also have bitter taste receptors,
you have salty taste receptors,
you have sour taste
receptors in your mouth
and of course, that means
your tongue and palate.
And those are interacting.
If you ingest a substance that's
just sweet or mostly sweet,
that causes a certain set of
effects on your blood glucose,
but also your brain, dopamine,
and the other neuro
circuits of your brain.
If you also ingest something that's sour
like lemon juice or lime juice,
it adjusts the output
of those neural circuits
in your brain.
So again, where you have a situation
where you have two parallel pathways,
one that's post-ingestive
coming from phenomenon
within our gut neurons,
but also things like
gastric emptying time,
the clearance and transfer of food,
and the conversion of food
into particular nutrients
and the circulation of
glucose in your bloodstream
and how it gets into the brain.
But also simply by
ingesting something sour,
you are changing the way
that sweet things impact your brain.
And so I think it stands to reason
that the lemon juice/lime juice effect
is not going to be magic.
It's going to have
everything to do with the way
that ingesting sour foods
can adjust the taste.
Excuse me, can adjust the neural response
to taste of sweet foods.
And in fact, we know based
on the beautiful work
of Charles Zuker at
Columbia Medical School,
that that's exactly what I happens.
They've measured the activity of neurons
at various locations in the so-called
taste pathways of the brain.
And they found that when particular tastes
like just sweet or just
bitter or just sour
evoke certain ensembles of neurons to fire
in particular sequences,
when sweet and sour are co-ingested,
when bitter and sour are co-ingested,
you get distinct ensembles,
meaning distinct patterns of
activity of those neurons.
And of course, distinct
patterns of downstream activity
within the brain and body.
So while it is still somewhat mysterious
as to how exactly things like
lemon juice and lime juice
can reduce our blood glucose spikes.
When we ingest those with sweet foods
or carbohydrate laden
foods, or with big meals,
you can use this as a tool
with the understanding
that there's a grounding in the biology
of the way these circuits work.
Now, some of you have
probably heard that cinnamon
can be a useful tool for
controlling blood sugar.
And indeed that's the case.
It's very clear that cinnamon can adjust
the rate of glucose entry into the stream,
possibly by changing the
rate of gastric emptying,
it might slow the rate of gastric emptying
and thereby also reduce the glycemic index
of particular foods.
So I suppose if I were
going to eat a mango,
and I hadn't just done a
bunch of hard training,
I might sprinkle some cinnamon on it here.
I always enjoy kind of
coming up with new ideas
of ways that I can eat
foods during these podcasts.
In any event, there's
some debate out there,
if you look online as to
whether or not Saigon Cinnamon,
Cassia cinnamon, excuse me,
or Ceylon cinnamon is best
for purposes of blunting
blood glucose spikes.
But I think the, at least
by my read of the data
and from what I've found,
it doesn't really matter
provided it's real cinnamon.
And you have to actually
look and make sure
that it's real cinnamon,
because a lot of cinnamon
that you buy is not real.
I do want to provide a cautionary
note about cinnamon however.
Cinnamon contains
something called coumarin.
which can be toxic at high levels.
So you don't want to ingest
more than about a teaspoon,
maybe a teaspoon and a
half of cinnamon per day,
because you'll start
to exceed the threshold
at which cinnamon could
start to be problematic.
But certainly if you're
going to have a big meal
or a meal that has a lot of sugar in it,
or a lot of carbohydrate laden foods,
and you don't want an
increase in blood glucose,
you could put cinnamon in a beverage,
you could put cinnamon on food
in order to blunt that
blood glucose increase,
reduce the glycemic index
by way of reducing gastric emptying time.
Again, just making sure
that you don't get out past
that one and a half teaspoons per day,
'cause you really don't
want to start dealing
with any of the toxicity
related to coumarin.
So we've talked about
lemon juice and lime juice
and cinnamon, these
are kind of commonplace
in many kitchens.
Then of course we can venture
into the more esoteric
or I would say the more advanced tools
for adjusting sugar intake.
And the one that comes to
mind is of course Berberine.
Berberine is a derivative of tree bark
and it is a very, very potent substance
for reducing blood glucose.
So much so that it is on par with
Metformin or Glibenclamide,
which are prescription
drugs specifically used
to reduce blood glucose.
So using Berberine is a serious step,
you should absolutely talk
to your doctor about it.
I know of a number of people that use it
to lower blood glucose when
they eat really large meals.
I know the number of
people that are using it
to get to some of the
other effects of Metformin
that people have discussed,
things like activating or
tapping into the so-called
AMPK pathway, reducing mTOR,
these are people that are
aiming their activities
at increasing longevity,
a somewhat controversial approach, still,
but I know many people are doing it.
It is true that if you ingest Berberine,
your blood glucose will plummet.
And I point that out because
I've actually tried it before,
it gave me brutal headaches
and I felt really dizzy,
and I felt like I couldn't see straight.
And actually I couldn't see
straight, why did it do that?
Well, it made me hypoglycemic.
It actually drove my blood
glucose down too far.
And the reason it did that
is that I took Berberine
on an empty stomach.
I know some people can tolerate it.
I would say, be very cautious
about ingesting Berberine
on an empty stomach,
or if you are in a low carbohydrate diet,
unless you really know what you're doing
and you have a medical professional
to kind of guide you through that.
If I took Berberine along
with a very large meal,
that included a lot of
carbohydrates, you know,
I can recall the days in
which Costello and I would eat
a couple of pizzas and then
we might get ice cream,
that kind of thing.
Then I felt perfectly fine
on even up to 750 milligrams
or a gram of Berberine.
It has the kind of unique
property of making you feel
not overwhelmed by the amount
of blood glucose increase
that you're experiencing
from eating a big meal.
I don't quite know how
else to describe it.
It's almost as if you can keep
eating and eating and eating,
and of course you have to
protect your gastric volume.
I mean, you only have so
much space in your stomach
to ingest food.
I wasn't using it to gorge on
food, I just heard about it,
I was interested in experimenting with it.
I don't have any chronic
blood sugar issues.
But again, when I took
it on an empty stomach,
it made me hypoglycemic on
a low carbohydrate intake,
hypoglycemic, not a good experience.
And again, an experience I think to avoid.
But provided there's a lot of
glucose in your bloodstream,
and certainly if you are
of the experimental type
or you're trying to
regulate blood glucose,
Berberine might be a good option.
But again, talk to your doctor.
It does have some other
interesting effects
in terms of lowering total cholesterol
that are research supported
of reducing insulin a little bit.
Well, that's not surprising
if you reduce blood glucose,
you're going to reduce
insulin because of course,
insulin manages blood
glucose in the bloodstream.
So I would place Berberine and of course,
Metformin and Glibenclamide in
the kind of the heavy hitting
potent tools for regulating blood glucose.
Now, this is an episode,
not about sugar per se,
but sugar viewed through the
lens of the nervous system.
And what's interesting about
Berberine, Metformin, Glibenclamide
and related substances,
is that some of the
effects are of course on
gastric emptying or
buffering blood glucose
within the bloodstream, et cetera.
But there appeared to also
be some neural effects
of having chronically low glucose
or blunting blood glucose
through things like Berberine.
And some of those neural effects include
longstanding changes in
the hormonal cascades
that are the consequence
of having low blood sugar
and thereby, changes
in the neural circuits
that manage blood glucose overall.
The simple way of saying
this is that by maintaining
low to moderate blood glucose,
either by not ingesting heavily
carbohydrate laden foods.
So here I'm speaking to the
low carb or the ketogenic types
or by blunting blood
glucose through things like
Metformin or Berberine,
even if ingesting carbohydrates,
maybe even some sugars,
over time, it seems that
there's a adjustment,
what we call a homeostatic regulation
of the neural circuits
that control things like
sugar craving, and indeed,
some people report feeling
fewer sugar cravings over time.
Now I didn't use Berberine for
a very long period of time,
I've never used Metformin.
I have experienced a somewhat
odd but welcome phenomenon
of with each progressive year of my life,
I have fewer and fewer sugar cravings.
Why that is, I don't know.
I suspect it might have
something to do with my sleep.
And I'll talk about that in a few minutes.
But if you're going to explore
Berberine or Metformin or otherwise,
in addition to working with a doctor,
I think you should understand
why you're doing it, right.
I think that many of the
effects can be quite potent.
They can happen in both the immediate term
in terms of regulating blood glucose,
they can send you hypoglycemic
if you aren't careful,
they can also cause longstanding changes
to the neural circuitry that regulates
blood sugar over time.
Some of which might be
welcome changes, right?
Reduce sugar cravings for instance.
And if you are really, really serious
about modulating blood glucose
through things like Berberine,
the typical dose range, again,
is anywhere from half a
gram to 1.5 grams daily,
that's the typical dosages
that have been explored.
And there are some other
substances like sodium caprate
which are known to augment
the effects of Berberine
via the AMPK pathways.
They basically can increase
the ability for Berberine
to have its glucose lowering actions.
But that of course is getting
into the really potent,
what I would call sharp blade tools
for controlling blood glucose.
And listen, anytime you're
dealing with blood glucose,
you are dealing with the brain's
preferred source of fuel.
And anytime you're dealing
with the brain's preferred source of fuel,
you have to be especially cautious
about depriving the
brain of what it needs.
So whether or not you're
low carb, high carb,
you know, keto, vegan,
carnivore, these substances,
like Berberine, are very, very potent
and you need to take them seriously.
There is yet another tool for
controlling sugar cravings
and the neural circuits
that regulate sugar craving
and its downstream consequences.
And this tool is what I would
call a high performance tool,
but it's one that you
probably didn't suspect
and that's sleep.
I've done extensive episodes about sleep,
and we actually have an episode
called master your sleep.
You can find that episode
easily at hubermanlab.com.
It's available in all the various formats,
YouTube, Apple, Spotify, et cetera.
and it provides a lot of tools.
And on social media, I
provide a lot of tools,
often we have a newsletter
that provides tools
on how to maximize sleep.
What is the role of sleep
in sugar metabolism,
sugar, hunger, and the way that the brain
regulates those things?
Well, there's a really
exciting study that came out
just last year.
This study was published in
the journal, Cell Report,
a Cell Press journal, excellent journal.
And the reason I love this study so much,
is it involved having people,
so yes, this was done in
humans, sleep in the laboratory.
That's not unusual, there's
a sleep lab at Stanford,
there's sleep labs elsewhere.
But what they did was
they actually measured
from the breath of these people,
and they extracted from their breath,
the metabolites that would allow them
to understand what sorts of metabolism
was occurring in these people's bodies
at different phases of sleep.
And this is a really remarkable study.
They actually did this every 10 seconds
throughout the entire night.
So in little tiny 10 second bits,
meaning at very high resolution,
they could evaluate what is the metabolism
in the brain and body
that people experience
as they go from REM sleep,
rapid eye movement sleep
to slow wave, sleep, and so on.
And I'll go deeper into the
study again in the future,
because it's so interesting,
and I think so important.
But what they discovered
was that each stage of sleep
was associated with a very
particular signature pattern
of metabolism and
particular phases of sleep
are associated with sugar metabolism,
or more with fat metabolism,
or more with other aspects of metabolism.
And the reason why I think
this study is important
to discuss in the context
of today's discussion
about sugar in the brain,
is that many people have experienced
the effects of disrupted
sleep on their appetite.
And in particular, it's been
reported that when people
are sleep deprived or the quality
of their sleep is disrupted,
that their appetite for
sugary food increases.
Now that was always assumed to
be due to some metabolic need
that was triggered by
the sleep deprivation
or by the poor sleep.
But in reading over this study,
some of the more important
points made by the authors
relate to the fact that well,
sleep is known to have
incredibly important effects
on brain and body, for
a variety of systems,
immune system, neural
functioning, et cetera.
This very organized sequence of particular
forms of metabolism being active
during particular phases of sleep,
which are very, very well orchestrated,
as we know, slow wave sleep, and REM sleep
being orchestrated in 90 minutes,
so-called ultradian cycles
and so on and so forth,
is thought to of perhaps
set up the brain and body
to be able to regulate
itself in the waking hours.
And therefore, when
people are sleep deprived
or deprived of certain forms
or states within sleep,
such as rapid eye movement sleep,
that it creates a disruption
in a particular set of metabolic pathways.
Now we don't a leap
too far from this study
to sugar metabolism
and the neural circuits
controlling sugar metabolism.
But I will say this, if
you look at the sum total
of the data on obesity
or on type two diabetes
or on metabolic syndromes of any kind,
you almost always see
disruptions in sleep.
Now, some of those could
be you do to sleep apnea
caused by even just the
size of somebody's neck
or the weight of their body.
In other words, we don't know
the direction of the effect,
metabolic syndromes could disrupt sleep,
which disrupt metabolic syndromes.
And indeed the authors point
out quite appropriately,
that they don't understand the direction
of the effects that they observe either.
But there is now a plethora
of data pointing to the fact
that getting quality sleep each night
helps regulate not only appetite,
but also the specific forms of metabolism
that drive specific appetites.
So the takeaway is,
while there are extravagant
and potent and interesting ways
to regulate blood glucose,
everything from cinnamon to
lemon juice, to Berberine,
to sodium caprate, to behavioral tools,
to the mere understanding of how
the direct and indirect pathways
go from the gut to dopamine, et cetera,
if you're not establishing
the firm foundation
of proper metabolism,
all of those things are going
to be sort of rearranging
deck chairs on the Titanic
as it's sometimes described.
So we can't overstate the importance
of getting regular sufficient
amount of high quality sleep,
at least 80% of the time,
not for sake of immune system
function, for clear thinking,
et cetera, but also for properly
regulating our metabolism,
including our sugar metabolism.
Thank you for joining
me for this discussion
about sugar and the nervous system
and how they are regulating each other
in both the brain and body.
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