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Picture warm, gooey cookies,

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crunchy candies, velvety cakes,

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waffle cones piled high with ice cream.

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Is your mouth watering?

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Are you craving dessert?

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Why?

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What happens in the brain
that makes sugary foods so hard to resist?

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Sugar is a general term
used to describe a class of molecules

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called carbohydrates,

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and it's found in a wide variety
of food and drink.

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Just check the labels
on sweet products you buy.

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Glucose, fructose, sucrose,

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maltose, lactose, dextrose, and starch

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are all forms of sugar.

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So are high-fructose corn syrup,

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fruit juice, raw sugar, and honey.

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And sugar isn't just
in candies and desserts,

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it's also added to tomato sauce,

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yogurt, dried fruit,
flavored waters, or granola bars.

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Since sugar is everywhere,
it's important to understand

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how it affects the brain.

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What happens when sugar hits your tongue?

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And does eating a little bit of sugar
make you crave more?

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You take a bite of cereal.

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The sugars it contains activate
the sweet-taste receptors,

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part of the taste buds on the tongue.

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These receptors send a signal
up to the brain stem,

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and from there, it forks off
into many areas of the forebrain,

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one of which is the cerebral cortex.

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Different sections of the cerebral cortex
process different tastes:

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bitter, salty, umami,

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and, in our case, sweet.

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From here, the signal activates
the brain's reward system.

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This reward system is a series
of electrical and chemical pathways

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across several different
regions of the brain.

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It's a complicated network,

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but it helps answer a single,
subconscious question:

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should I do that again?

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That warm, fuzzy feeling you get
when you taste Grandma's chocolate cake?

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That's your reward system saying,

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"Mmm, yes!"

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And it's not just activated by food.

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Socializing, sexual behavior, and drugs

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are just a few examples
of things and experiences

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that also activate the reward system.

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But overactivating this reward system
kickstarts a series of unfortunate events:

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loss of control, craving,
and increased tolerance to sugar.

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Let's get back to our bite of cereal.

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It travels down into your stomach
and eventually into your gut.

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And guess what?

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There are sugar receptors here, too.

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They are not taste buds,
but they do send signals

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telling your brain that you're full

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or that your body should
produce more insulin

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to deal with the extra sugar
you're eating.

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The major currency
of our reward system is dopamine,

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an important chemical or neurotransmitter.

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There are many dopamine
receptors in the forebrain,

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but they're not evenly distributed.

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Certain areas contain dense
clusters of receptors,

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and these dopamine hot spots
are a part of our reward system.

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Drugs like alcohol, nicotine, or heroin

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send dopamine into overdrive,

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leading some people
to constantly seek that high,

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in other words, to be addicted.

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Sugar also causes dopamine to be released,
though not as violently as drugs.

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And sugar is rare
among dopamine-inducing foods.

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Broccoli, for example, has no effect,

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which probably explains

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why it's so hard to get
kids to eat their veggies.

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Speaking of healthy foods,

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let's say you're hungry
and decide to eat a balanced meal.

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You do, and dopamine levels spike
in the reward system hot spots.

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But if you eat that same dish
many days in a row,

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dopamine levels will spike less and less,
eventually leveling out.

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That's because when it comes to food,

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the brain evolved to pay special attention
to new or different tastes.

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Why?

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Two reasons:

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first, to detect food that's gone bad.

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And second, because the more variety
we have in our diet,

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the more likely we are
to get all the nutrients we need.

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To keep that variety up,

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we need to be able
to recognize a new food,

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and more importantly, we need
to want to keep eating new foods.

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And that's why the dopamine levels off
when a food becomes boring.

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Now, back to that meal.

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What happens if in place
of the healthy, balanced dish,

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you eat sugar-rich food instead?

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If you rarely eat sugar
or don't eat much at a time,

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the effect is similar
to that of the balanced meal.

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But if you eat too much,
the dopamine response does not level out.

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In other words, eating lots of sugar
will continue to feel rewarding.

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In this way, sugar behaves
a little bit like a drug.

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It's one reason people seem
to be hooked on sugary foods.

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So, think back to all those
different kinds of sugar.

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Each one is unique,
but every time any sugar is consumed,

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it kickstarts a domino effect in the brain
that sparks a rewarding feeling.

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Too much, too often,
and things can go into overdrive.

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So, yes, overconsumption of sugar
can have addictive effects on the brain,

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but a wedge of cake once
in a while won't hurt you.