0:00:06.825,0:00:09.101
Picture warm, gooey cookies,

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crunchy candies,

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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?

0:00:18.843,0:00:19.924
What happens in the brain

0:00:19.924,0:00:23.700
that makes sugary foods so hard to resist?

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Sugar is a general term

0:00:24.421,0:00:26.549
used to describe a class of molecules

0:00:26.549,0:00:28.427
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,

0:00:34.913,0:00:35.695
fructose,

0:00:35.695,0:00:36.627
sucrose,

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maltose,

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lactose,

0:00:38.295,0:00:38.969
dextrose,

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and starch

0:00:39.681,0:00:41.445
are all forms of sugar.

0:00:41.445,0:00:43.525
So are high-fructose corn syrup,

0:00:43.525,0:00:44.309
fruit juice,

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raw sugar,

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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,

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dried fruit,

0:00:52.777,0:00:53.856
flavored waters,

0:00:53.856,0:00:55.700
or granola bars.

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Since sugar is everywhere,

0:00:56.603,0:00:58.026
it's important to understand

0:00:58.026,0:00:59.906
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

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make you crave more?

0:01:05.480,0:01:07.025
You take a bite of cereal.

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The sugars it contains

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activate the sweet taste receptors,

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part of the taste buds on the tongue.

0:01:12.770,0:01:15.771
These receptors send a signal up to the brain stem,

0:01:15.771,0:01:17.375
and from there, it forks off

0:01:17.375,0:01:19.261
into many areas of the forebrain,

0:01:19.261,0:01:21.813
one of which is the cerebral cortex.

0:01:21.813,0:01:23.964
Different sections of the cerebral cortex

0:01:23.964,0:01:25.864
process different tastes:

0:01:25.864,0:01:26.399
bitter,

0:01:26.399,0:01:26.985
salty,

0:01:26.985,0:01:27.711
umami,

0:01:27.711,0:01:29.823
and, in our case, sweet.

0:01:29.823,0:01:31.328
From here, the signal activates

0:01:31.328,0:01:33.440
the brain's reward system.

0:01:33.440,0:01:34.909
This reward system is a series

0:01:34.909,0:01:37.125
of electrical and chemical pathways

0:01:37.125,0:01:39.749
across several different regions of the brain.

0:01:39.749,0:01:40.873
It's a complicated network,

0:01:40.873,0:01:44.171
but it helps answer a single, subconscious question:

0:01:44.171,0:01:45.877
should I do that again?

0:01:45.877,0:01:47.413
That warm, fuzzy feeling you get

0:01:47.413,0:01:49.501
when you taste Grandma's chocolate cake?

0:01:49.501,0:01:51.295
That's your reward system saying,

0:01:51.295,0:01:52.753
"Mmm, yes!"

0:01:52.753,0:01:55.090
And it's not just activated by food.

0:01:55.090,0:01:55.935
Socializing,

0:01:55.935,0:01:56.795
sexual behavior,

0:01:56.795,0:01:57.469
and drugs

0:01:57.469,0:01:58.931
are just a few examples

0:01:58.931,0:02:00.346
of things and experiences

0:02:00.346,0:02:02.959
that also activate the reward system.

0:02:02.959,0:02:05.145
But overactivating this reward system

0:02:05.145,0:02:08.435
kickstarts a series of unfortunate events:

0:02:08.435,0:02:09.268
loss of control,

0:02:09.268,0:02:10.200
craving,

0:02:10.200,0:02:12.711
and increased tolerance to sugar.

0:02:12.711,0:02:14.963
Let's get back to our bite of cereal.

0:02:14.963,0:02:17.069
It travels down into your stomach

0:02:17.069,0:02:18.912
and eventually into your gut.

0:02:18.912,0:02:19.949
And guess what?

0:02:19.949,0:02:22.380
There are sugar receptors here, too.

0:02:22.380,0:02:23.335
They are not taste buds,

0:02:23.335,0:02:24.755
but they do send signals

0:02:24.755,0:02:26.587
telling your brain that you're full

0:02:26.587,0:02:28.709
or that your body should produce more insulin

0:02:28.709,0:02:31.003
to deal with the extra sugar you're eating.

0:02:31.003,0:02:32.428
The major currency

0:02:32.428,0:02:34.563
of our reward system is dopamine,

0:02:34.563,0:02:37.153
an important chemical or neurotransmitter.

0:02:37.153,0:02:39.684
There are many dopamine receptors in the forebrain,

0:02:39.684,0:02:41.840
but they're not evenly distributed.

0:02:41.840,0:02:44.648
Certain areas contain dense clusters of receptors,

0:02:44.648,0:02:46.312
and these dopamine hot spots

0:02:46.312,0:02:48.481
are a part of our reward system.

0:02:48.481,0:02:49.767
Drugs like alcohol,

0:02:49.767,0:02:50.436
nicotine,

0:02:50.436,0:02:51.361
or heroin

0:02:51.361,0:02:53.366
send dopamine into overdrive,

0:02:53.366,0:02:56.449
leading some people to constantly seek that high,

0:02:56.449,0:02:58.645
in other words, to be addicted.

0:02:58.645,0:03:01.071
Sugar also causes dopamine to be released,

0:03:01.071,0:03:03.238
though not as violently as drugs.

0:03:03.238,0:03:06.400
And sugar is rare among dopamine-inducing foods.

0:03:06.400,0:03:08.652
Broccoli, for example, has no effect,

0:03:08.652,0:03:09.738
which probably explains

0:03:09.738,0:03:12.837
why it's so hard to get kids to eat their veggies.

0:03:12.837,0:03:14.416
Speaking of healthy foods,

0:03:14.416,0:03:15.620
let's say you're hungry

0:03:15.620,0:03:17.597
and decide to eat a balanced meal.

0:03:17.597,0:03:19.683
You do, and dopamine levels spike

0:03:19.683,0:03:21.349
in the reward system hot spots.

0:03:21.349,0:03:24.730
But if you eat that same dish many days in a row,

0:03:24.730,0:03:27.063
dopamine levels will spike less and less,

0:03:27.063,0:03:28.998
eventually leveling out.

0:03:28.998,0:03:30.643
That's because when it comes to food,

0:03:30.643,0:03:33.077
the brain evolved to pay special attention

0:03:33.077,0:03:34.955
to new or different tastes.

0:03:34.955,0:03:35.900
Why?

0:03:35.900,0:03:37.070
Two reasons:

0:03:37.070,0:03:39.444
first, to detect food that's gone bad.

0:03:39.444,0:03:41.731
and second, because the more variety

0:03:41.731,0:03:42.753
we have in our diet,

0:03:42.753,0:03:43.840
the more likely we are

0:03:43.840,0:03:45.876
to get all the nutrients we need.

0:03:45.876,0:03:47.251
To keep that variety up,

0:03:47.251,0:03:49.663
we need to be able to recognize a new food,

0:03:49.663,0:03:50.839
and more importantly,

0:03:50.839,0:03:53.544
we need to want to keep eating new foods.

0:03:53.544,0:03:55.505
And that's why the dopamine levels off

0:03:55.505,0:03:57.367
when a food becomes boring.

0:03:57.367,0:03:58.966
Now, back to that meal.

0:03:58.966,0:04:00.423
What happens if in place

0:04:00.423,0:04:02.092
of the healthy, balanced dish,

0:04:02.092,0:04:04.307
you eat sugar-rich food instead?

0:04:04.307,0:04:05.840
If you rarely eat sugar

0:04:05.840,0:04:07.339
or don't eat much at a time,

0:04:07.339,0:04:09.973
the effect is similar to that of the balanced meal.

0:04:09.973,0:04:11.174
But if you eat too much,

0:04:11.174,0:04:13.726
the dopamine response does not level out.

0:04:13.726,0:04:15.493
In other words, eating lots of sugar

0:04:15.493,0:04:17.745
will continue to feel rewarding.

0:04:17.745,0:04:21.153
In this way, sugar behaves a little bit like a drug.

0:04:21.153,0:04:22.933
It's one reason people seem to be hooked

0:04:22.933,0:04:24.621
on sugary foods.

0:04:24.621,0:04:27.267
So, think back to all those different kinds of sugar.

0:04:27.267,0:04:28.740
Each one is unique,

0:04:28.740,0:04:30.928
but every time any sugar is consumed,

0:04:30.928,0:04:33.382
it kick-starts a domino effect in the brain

0:04:33.382,0:04:35.289
that sparks a rewarding feeling.

0:04:35.289,0:04:36.544
Too much, too often,

0:04:36.544,0:04:38.720
and things can go into overdrive.

0:04:38.720,0:04:40.922
So, yes, overconsumption of sugar

0:04:40.922,0:04:42.975
can have addictive effects on the brain,

0:04:42.975,0:04:46.178
but a wedge of cake once in a while won't hurt you.