- 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.

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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