and it's finally cold enough to wear my favorite winter sweater and jacket and beanie and gloves.

終於冷到可以穿我最喜歡的冬季毛衣、夾克、毛帽和手套了。

And I drink pumpkin spice lattes to stay warm.

我喝著南瓜風味拿鐵取暖。

But I also love the feeling when it's the middle of winter and out of nowhere it's 55 degrees.

我也喜歡冬天時，氣溫忽然上升到 13 度，

So I leave my parka home and go outside in my shorts and t-shirt

所以我把防寒大衣留在家裡，穿著短褲和踢恤出門，

and I feel the warmth of the sun on my skin.

感受陽光照在皮膚上的溫度。

And I consider going to the beach to tan because it's so warm.

還想著去海灘晒太陽，因為天氣真的很溫暖。

The temperature is the same, but my reaction to it is vastly different.

溫度一樣，但我的反應卻大不同。

Part of the reason why is that there's more of a substance in my body in January as compared to September.

部分原因是 1 月時，我體內某種物質含量比 9 月時來得多。

It's the same substance that allows kids and teens to handle the cold weather better than adults.

正是這種物質讓兒童和青少年比成年人更能抵禦寒冷。

When you're hot, you sweat.

熱的時候，會出汗。

When you're cold, you shiver.

冷的時候，會發抖。

But just before you start to shiver, your body actually does something else.

但在開始發抖前，身體其實還會發生一件事。

It starts to burn fat.

那就是燃燒脂肪。

But not the fat we usually think of.

但不是我們通常認為的那種脂肪。

There are two categories of fat that we like to think about.

常見的脂肪有兩類，

There's the white fat.

一種是「白色脂肪」。

White fat is the one that we tend to just think of as "fat".

白脂肪就是我們通常指的「脂肪」。

It's called white because it looks white.

名字就是由其顏色而來。

White fat exists all throughout the body,

白色脂肪遍佈全身，

cushioning our bones and organs.

作為骨骼和器官的緩衝。

That's Dr. Aaron Cypess, by the way.

順帶一提，剛剛那是亞倫·賽普斯博士。

White fat cells have many functions.

白色脂肪細胞有許多功能，

One of the most important being that they're the body's primary energy source.

其中最重要的一點是，它們是身體的主要能量來源。

Every single day we are using the fuel that's inside the white fat cells.

每天，我們都在消耗白色脂肪細胞內物質的能量。

But there's another type of fat that has a totally different function:

但還有另一種脂肪具有完全不同的功能，

Brown fat.

那就是棕色脂肪。

These cells are much smaller,

這些細胞要小得多，

and because of that, resemble muscle more than fat.

正因如此，它更像肌肉而不是脂肪。

Instead of one large lipid droplet in a white fat cell,

不像白色脂肪細胞裡面是一個大脂質液滴，

the brown fat cell is one tightly packed bag of mitochondria.

棕色脂肪細胞是個密密麻麻的線粒體袋。

This is what gives it its brown appearance.

這就是其外觀呈棕色的原因。

And if you remember anything from high school biology class,

如果你還記得高中生物課上的內容，

you know that the mitochondria are the powerhouse of the cell.

就會知道線粒體是「細胞的發電站」。

Brown fat, instead of serving as an energy reserve for organs throughout the body to burn,

棕色脂肪並不是全身器官的能量儲備庫，

uses its power to burn energy on its own.

而是用其自身力量自行產生能量。

And unlike white fat, it's only located in a few tactically positioned areas.

且不像白色脂肪，棕色脂肪只分佈於幾個重要區域。

It is in the neck, the shoulders, in the upper arms.

分別是頸部、肩部、上臂，

It's down the spine and then some places within the belly.

圍繞脊柱，以及腹部某些地方。

Lots of overlap with major blood vessels

其分佈與主要血管有很多重疊處，

because warming the blood effectively warms the whole body.

因為溫暖了血液就能有效讓全身升溫。

The brown fat around the neck vessels heats up the blood, goes to the brain.

頸部血管周圍的棕色脂肪會加熱其血液，而它們會流向大腦。

That's good.

這很好。

The brown fat depots in the shoulders.

肩部的褐色脂肪庫所加熱的血液，

That blood, once it's been heated by the brown fat goes right — very quickly, into the heart

這些血液加熱後會迅速進入心臟，

and then can get pumped to the rest of the body.

然後被泵送到身體各處。

And that's the first line of defense against the cold.

這就是抵禦寒冷的第一道防線。

If it's not enough to raise the body temperature sufficiently...

如果這還不足以充分提高體溫…

then the body shivers.

身體才會顫抖。

But one of the craziest things that I learned while researching this story is that...

但我在研究這件事時，瞭解到最瘋狂的事是…

babies can't shiver.

嬰兒不會發抖。

When babies are born, they do not have the muscle mass

嬰兒剛出生時沒有足夠的肌肉量，

and perhaps not even so much of the coordination with the brain and the muscle to shiver effectively.

甚至可能大腦和肌肉的協調能力也不足以支撐他們發抖。

So they need other ways of generating heat,

所以他們需要以其他方式發熱，

and brown fat is part of that.

棕色脂肪就是其中一種方式。

Babies are born with a lot of brown fat.

嬰兒從出生就有大量棕色脂肪。

According to the Cleveland Clinic,

克利夫蘭診所指出，

about 2 to 5% of a baby's body weight is made up of this stuff.

嬰兒體重的百分之 2 至 5 是由此物質構成。

It's necessary for our survival.

棕色脂肪為支撐人類存活必要之物。

The peak age for brown fat actually seems to be in the teen years,

人體棕色脂肪含量最多的時期似乎是青少年階段，

which explains why a lot of the guys in my high school wore shorts in the winter.

這也解釋了為什麼高中很多男生冬天的時還可以穿短褲。

But as we get older, our body makes less of it.

但隨年齡增長，體內棕色脂肪會逐漸減少。

And this could give us some insight into why kids seem to run hot

這可以讓我們稍微了解為何孩子們總是很熱，

and our parents or grandparents seem to run cold.

而我們的父母或祖父母卻似乎常常發冷。

Older people, they certainly have much less brown fat in terms of absolute and relative amounts.

老年人顯然有更少的棕色脂肪，不論是單看數字還是相對來說。

There's also less muscle,

他們的肌肉量也較少，

which is also important for generating heat.

而肌肉對產生熱量也很重要。

The similarities between brown fat and muscle don't end there, though.

不過棕色脂肪和肌肉之間的相似之處不僅止於此。

If you work your brown fat out, it also increases volume.

像鍛鍊肌肉一樣，如果鍛煉棕色脂肪，它也會增加。

And the way you do this is by exposing yourself to the cold for extended periods of time

鍛鍊的方法是讓自己長時間暴露於寒冷中，

as this 2014 study shows.

正如這項 2014 年的研究所顯示的。

Look at how much more brown fat these men from Maryland had after a month of exposure to cold temperatures.

看看這些來自馬里蘭州的男性在暴露於低溫一個月後，棕色脂肪增加了多少。

And look how much less they had when exposed to warm temperatures.

再看看當他們處於溫暖的溫度下時，棕色脂肪又減少了多少。

Which gives us some insight into why 55 degrees in the winter can feel so much warmer than 55 degrees in the fall.

這也解釋了為何同樣是 13 度，冬天的體感卻比秋天暖和得多。

Brown fat doesn't just keep you warm, though.

但棕色脂肪的作用不只有保暖。

Scientists have figured out that having more of it correlates to lower risk of diabetes and heart disease.

科學家們發現，棕色脂肪越多，患糖尿病和心髒病風險就越低。

Studying the effects of brown fat using cold exposure is challenging, though.

但用寒冷暴露法研究棕色脂肪對人體的影響實際上困難重重。

One challenge is that it's hard to dose cold.

其中一個原因是寒冷很難「配給」。

How much... I gave you this amount of cold,

多少量… 要給你多少寒冷…

I mean, you know the temperature,

我的意思是，我們知道溫度，

but it's hard to know what you're doing

但難以知曉身體運作，

and therefore it's very hard to design a study where it's reproducible.

所以設計一項可重複的實驗是非常困難的。

So instead,

因此，相反的，

they're trying to activate brown fat with medicine to study how burning it affects us biologically.

科學家們正試圖用藥物活化棕色脂肪，研究其燃燒對人的影響。

A medication called Mirabegron,

這種藥物叫貝坦利，

which is approved to treat overactive bladder,

該藥已經準許用於治療膀胱過動症，

was able to activate the brown fat in a way that was very similar to the effectiveness of the cold exposure.

能以與寒冷暴露法非常相似的方式活化棕色脂肪。

There's a lot we still don't know about brown fat,

關於棕色脂肪，目前仍有很多未知之處，

but we do know that our bodies use it to adapt to cold weather.

但能確信的是，身體會依靠它來適應寒冷。

And when a kid doesn't want to put a coat on in the winter,

所以如果一個孩子冬天不想穿外套，

it's not necessarily that they're just stubborn.

不一定是他固執，

It might just be because they have a little more of something in their body than you do.

可能只是因為他們體內的棕色脂肪比你多。