Is your mouth watering?

流口水了嗎？

Are you craving dessert?

想來點甜點？

Why?

為什麼？

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

什麼影響腦部讓甜食如此難以抗拒？

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.

糖是「碳水化合物」的俗稱， 存在於各種食物及飲料中。

Just check the labels on sweet products you buy.

看看甜品上的標籤就知道了。

Glucose, fructose, sucrose, maltose, lactose, dextrose, and starch are all forms of sugar.

葡萄糖、果糖、蔗糖、麥芽糖、乳糖、右旋葡萄糖及澱粉都是糖的不同形式。

So are high-fructose corn syrup, fruit juice, raw sugar, and honey.

高果糖玉米糖漿、果汁、粗糖還有蜂蜜也是。

And sugar isn't just in candies and desserts, it's also added to tomato sauce, yogurt, dried fruit, flavored waters, or granola bars.

糖不止存於糖果與甜點中，番茄醬、優格、水果乾、調味水和燕麥棒都有加糖。

Since sugar is everywhere, it's important to understand how it affects the brain.

因為糖類無所不在，所以了解它如何影響大腦就很重要了。

What happens when sugar hits your tongue?

當糖類碰到舌頭時會發生什麼事？

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

吃一點點糖就會讓你想吃更多嗎？

You take a bite of cereal.

你吃下一口麥片。

The sugars it contains activate the sweet taste receptors, part of the taste buds on the tongue.

裡面的糖份活化了甜味的受器，也就是舌頭上味蕾的一部份。

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.

這些受器傳送訊號給腦幹，訊號分叉進入前腦各個區域，其中一處為大腦皮質。

Different sections of the cerebral cortex process different tastes:

大腦皮質不同部份會處理不同味覺：

bitter, salty, umami, and, in our case, sweet.

苦味、鹹味、鮮味，還有我們正在談的甜味。

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

在這裡，訊號活化大腦的「獎勵系統」

This reward system is a series of electrical and chemical pathways across several different regions of the brain.

獎勵系統為一連串縱橫大腦不同區域的電化學路徑。

It's a complicated network, but it helps answer a single, subconscious question:

它是一個複雜的網絡，幫助我們回答一個潛意識中的問題：

should I do that again?

該再做一次嗎？

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

品嚐祖母做的巧克力蛋糕時，那熱騰騰、黏糊糊的感覺是什麼？

That's your reward system saying, "Mmm, yes!"

是獎勵系統在說「嗯，太棒了！」

And it's not just activated by food.

不光食物可以活化獎勵系統。

Socializing, sexual behavior, and drugs are just a few examples of things and experiences that also activate the reward system.

其中還有社交活動、性行為、藥物都是能活化獎勵系統。

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

但過度活化獎勵系統會促使一連串不幸發生：

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

失控、渴求、對糖的耐受性增加。

Let's get back to our bite of cereal.

回到剛剛提的麥片。

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

麥片穿過胃，最終進入腸道。

And guess what?

猜猜怎麼著？

There are sugar receptors here, too.

這裡也有糖類受器。

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.

雖然它們不是味蕾，但也會傳送訊號告訴大腦，你飽了或身體該製造更多胰島素去處理多餘的糖份。

The major currency of our reward system is dopamine, an important chemical or neurotransmitter.

獎勵系統中主要的傳遞物質叫「多巴胺」， 一個很重要的化學、神經傳導物質。

There are many dopamine receptors in the forebrain, but they're not evenly distributed.

前腦有許多多巴胺受器，但它們並不均勻分佈於前腦。

Certain areas contain dense clusters of receptors, and these dopamine hot spots are a part of our reward system.

某些區域受器密度高，這些多巴胺集中區就是獎勵系統的一部份。

Drugs like alcohol, nicotine, or heroin send dopamine into overdrive, leading some people to constantly seek that high, in other words, to be addicted.

藥物如酒精、尼古丁或海洛因會產生超量多巴胺，導致某些人不斷尋找同樣的興奮感，也就是「上癮了」

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

糖也會引起大腦釋放多巴胺，但沒有藥物那麼強烈。

And sugar is rare among dopamine-inducing foods.

而糖就是其中少數會引起釋放多巴胺的食物，

Broccoli, for example, has no effect, which probably explains why it's so hard to get kids to eat their veggies.

例如花椰菜，就沒有刺激多巴胺的作用，這解釋了為什麼孩子們不喜歡吃蔬菜。

Speaking of healthy foods, let's say you're hungry and decide to eat a balanced meal.

談到健康食物，假如你決定要吃營養均衡的一餐。

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

這麼做時，多巴胺量會衝高並刺激獎勵系統集中區。

But if you eat that same dish many days in a row, dopamine levels will spike less and less, eventually leveling out.

但假如你連續好幾天吃同樣菜色，多巴胺釋放量將愈來愈低，最後消失。

That's because when it comes to food, the brain evolved to pay special attention to new or different tastes.

這是因為大腦演進成會被新奇、多樣的口味吸引。

Why?

為什麼？

Two reasons.

兩個原因：

First, to detect food that's gone bad.

首先，為了辨識食物有沒有變質。

And second, because the more variety we have in our diet, the more likely we are to get all the nutrients we need.

再來是因為吃得愈多樣性，就愈有可能攝取到人體所需的營養。

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.

為提升多樣化，我們需要有辨認新食物的能力，更重要的是，我們必須「想」去嚐試新食物。

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

這就是為什麼當食物一成不變時，多巴胺量會停止波動。

Now, back to that meal.

回到我們提到的那一餐。

What happens if in place of the healthy, balanced dish, you eat sugar-rich food instead?

如果用高糖份食物替代健康、均衡的飲食會怎樣呢？

If you rarely eat sugar or don't eat much at a time, the effect is similar to that of the balanced meal.

如果你很少吃甜食，或一次吃得不多，結果和均衡飲食就會差不多。

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

但如果你攝取過多甜食，多巴胺反應就不會消失。

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

換句話說，攝取過量的糖獎勵的歡快感將會一直持續。

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

如此，糖變得像藥物一樣。

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

這就是人們對高糖份食品成癮的原因之一。

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

因此，想想開頭提到的各種糖。

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.

各個都獨一無二，但不管吃什麼糖都會引起腦內骨牌效應，產生歡愉感。

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

吃太多或太頻繁，身體會無法負荷。

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.

所以雖然過度攝取糖類會成癮，但偶爾來一小塊蛋糕無傷大雅。