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  • Picture warm, gooey cookies,

  • crunchy candies,

  • velvety cakes,

  • waffle cones piled high with ice cream.

  • Is your mouth watering?

  • Are you craving dessert?

  • Why?

  • What happens in the brain

  • that makes sugary foods so hard to resist?

  • Sugar is a general term

  • used to describe a class of molecules

  • called carbohydrates,

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

  • Just check the labels on sweet products you buy.

  • Glucose,

  • fructose,

  • sucrose,

  • maltose,

  • lactose,

  • dextrose,

  • and starch

  • are all forms of sugar.

  • So are high-fructose corn syrup,

  • fruit juice,

  • raw sugar,

  • and honey.

  • And sugar isn't just in candies and desserts,

  • it's also added to tomato sauce,

  • yogurt,

  • dried fruit,

  • flavored waters,

  • or granola bars.

  • Since sugar is everywhere,

  • it's important to understand

  • how it affects the brain.

  • What happens when sugar hits your tongue?

  • And does eating a little bit of sugar

  • make you crave more?

  • You take a bite of cereal.

  • The sugars it contains

  • activate the sweet taste receptors,

  • part of the taste buds on the tongue.

  • These receptors send a signal up to the brain stem,

  • and from there, it forks off

  • into many areas of the forebrain,

  • one of which is the cerebral cortex.

  • Different sections of the cerebral cortex

  • process different tastes:

  • bitter,

  • salty,

  • umami,

  • and, in our case, sweet.

  • From here, the signal activates

  • the brain's reward system.

  • This reward system is a series

  • of electrical and chemical pathways

  • across several different regions of the brain.

  • It's a complicated network,

  • but it helps answer a single, subconscious question:

  • should I do that again?

  • That warm, fuzzy feeling you get

  • when you taste Grandma's chocolate cake?

  • That's your reward system saying,

  • "Mmm, yes!"

  • And it's not just activated by food.

  • Socializing,

  • sexual behavior,

  • and drugs

  • are just a few examples

  • of things and experiences

  • that also activate the reward system.

  • But overactivating this reward system

  • kickstarts a series of unfortunate events:

  • loss of control,

  • craving,

  • and increased tolerance to sugar.

  • Let's get back to our bite of cereal.

  • It travels down into your stomach

  • and eventually into your gut.

  • And guess what?

  • There are sugar receptors here, too.

  • They are not taste buds,

  • but they do send signals

  • telling your brain that you're full

  • or that your body should produce more insulin

  • to deal with the extra sugar you're eating.

  • The major currency

  • of our reward system is dopamine,

  • an important chemical or neurotransmitter.

  • There are many dopamine receptors in the forebrain,

  • but they're not evenly distributed.

  • Certain areas contain dense clusters of receptors,

  • and these dopamine hot spots

  • are a part of our reward system.

  • Drugs like alcohol,

  • nicotine,

  • or heroin

  • send dopamine into overdrive,

  • leading some people to constantly seek that high,

  • in other words, to be addicted.

  • Sugar also causes dopamine to be released,

  • though not as violently as drugs.

  • And sugar is rare among dopamine-inducing foods.

  • Broccoli, for example, has no effect,

  • which probably explains

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

  • Speaking of healthy foods,

  • let's say you're hungry

  • and decide to eat a balanced meal.

  • You do, and dopamine levels spike

  • in the reward system hot spots.

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

  • dopamine levels will spike less and less,

  • eventually leveling out.

  • That's because when it comes to food,

  • the brain evolved to pay special attention

  • to new or different tastes.

  • Why?

  • Two reasons:

  • first, to detect food that's gone bad.

  • and second, because the more variety

  • we have in our diet,

  • the more likely we are

  • to get all the nutrients we need.

  • To keep that variety up,

  • we need to be able to recognize a new food,

  • and more importantly,

  • we need to want to keep eating new foods.

  • And that's why the dopamine levels off

  • when a food becomes boring.

  • Now, back to that meal.

  • What happens if in place

  • of the healthy, balanced dish,

  • you eat sugar-rich food instead?

  • If you rarely eat sugar

  • or don't eat much at a time,

  • the effect is similar to that of the balanced meal.

  • But if you eat too much,

  • the dopamine response does not level out.

  • In other words, eating lots of sugar

  • will continue to feel rewarding.

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

  • It's one reason people seem to be hooked

  • on sugary foods.

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

  • Each one is unique,

  • but every time any sugar is consumed,

  • it kick-starts a domino effect in the brain

  • that sparks a rewarding feeling.

  • Too much, too often,

  • and things can go into overdrive.

  • So, yes, overconsumption of sugar

  • can have addictive effects on the brain,

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

Picture warm, gooey cookies,

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TED-ED】糖質が脳に与える影響 - ニコル・アヴェナ (【TED-Ed】How sugar affects the brain - Nicole Avena)

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    Halu Hsieh に公開 2021 年 01 月 14 日
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