Olive oil is 100% fat; there's nothing else in it.

橄榄油含有100%的脂肪，除此之外没有别的。

Pancake mix, on the other hand, is only about 11% fat.

相反，煎饼只有约11%的脂肪，

And, yet, olive oil is good for you, and pancake mix is not.

然而，橄榄油对你的身体有益，煎饼则不然。

Why is that?

为什么会这样呢？

As it turns out,

原来，

the amount of fat we eat doesn't impact our weight or our cholesterol or our risk of heart disease nearly as much as what kind of fat we eat.

我们摄入的脂肪含量并不影响我们的体重，或我们的胆固醇，或我们得心脏病的机率，而这些只是跟我们摄入的脂肪种类有关。

But let's back up: What is fat?

不过我们先回过头来：什么是脂肪？

If we were to zoom in on a salmon, which is a fatty fish, past the organs, past the tissues, into the cells,

如果我们把三文鱼放大来看，三文鱼是一种脂肪很多的鱼，不看内脏，不看组织，只看细胞，

we would see that the stuff we call fat is actually made up of molecules called triglycerides, and they are not all alike.

我们就会看到我们称之为脂肪的东西其实是是由一种叫三酸甘油酯的分子所组成的，而这些分子并不完全相似。

Here's one example.

这里举一个例子。

Those three carbons on the left, that's glycerol.

左边的那三颗碳，是甘油，

Now, you can think of that as the backbone that holds the rest of the molecule together.

你可以把它想像成骨干，它能够把其它的分子紧紧连在一起。

The three long chains on the right are called fatty acids,

右边的那三条长链被称为脂肪酸，

and it's subtle differences in the structures of these chains that determine whether a fat is, let's say, solid or liquid;

这些分子链结构的微妙差别决定了某种脂肪比如说，是固体的还是液体的，

whether or not it goes rancid quickly; and, most importantly, how good or how bad it is for you.

是否会很快变质，最重要的是，对你是有益的还是有害的。

Let's take a look at some of these differences.

让我们来看看这些差别。

One is length.

一个是长度，

Fatty acids can be short or long.

脂肪酸可长可短。

Another, more important difference is the type of bond between the carbon atoms.

另一个更重要的区别是连接碳原子的碳键的形式。

Some fatty acids have only single bonds.

有些脂肪酸只有单键，

Others have both single and double bonds.

另外一些则同时拥有单键和双键。

Fatty acids with only single bonds are called saturated, and those with one or more double bonds are called unsaturated.

只有单键的脂肪酸为饱和脂肪酸，有单个或多个双键的脂肪酸则为不饱和脂肪酸。

Now, most unsaturated fats are good for you, while saturated fats are bad for you in excess.

大部分的不饱和脂肪酸对人体是有益的，而过多的饱和脂肪酸则是有害的。

For saturated fats, the story pretty much ends there but not for unsaturated fats.

就饱和脂肪酸而言，基本上就是这样。就不饱和脂肪酸而言，

The double bonds in these molecules have a kind of weird property; they're rigid.

双键在这些分子中有一种奇怪的特性，它们有十分坚固的刚性结构。

So, that means there are two ways to arrange every double bond.

这意味着有两种排列组合双键的方式。

The first is like this, where both hydrogens are on same side and both carbons are on the same side.

第一种就像这样，两颗氢都在同一边，两颗碳也在同一边。

The second way is like this.

第二种方式像这样，

Now the hydrogens and carbons are on opposite sides of the double bond.

氢和碳在双键对立的两端。

Now, even though both of these molecules are made up of exactly the same building blocks, they are two completely different substances,

尽管这两种分子由一模一样的东西组成，它们是完全不同的物质，

and they behave completely differently inside of us.

在我们体内也表现得完全不同。

The configuration on the left is called CIS, which you've probably never heard of.

左边的这个结构称为顺式异构体 (CIS)，你可能从来也没听过。

The one of the right is called TRANS, and you probably have heard of trans fats before.

右边的这个称为反式异构体 (TRANS)，你以前可能有听过反式脂肪，

They don't go rancid, they're more stable during deep frying, and they can change the texture of foods in ways that other fats just can't.

它们不容易变质，它们在油炸时比较稳定，而且它们可以改变食物的口感，这是其它种类的脂肪无法做到的。

They're also terrible for your health, by far worse than saturated fat, even though technically they're a type of unsaturated fat.

但是它们非常不益健康，比饱和脂肪还要坏，虽然严格来说，它们是不饱和脂肪的一种。

Now, I know that seems crazy, but your body doesn't care what a molecule looks like on paper.

我知道，这听上去很不可思议，但是你的身体可不管某个分子在纸上的样子，

All that matters is the 3-D shape where the molecule fits, where it doesn't, and what pathways it interferes with.

它只在乎它们的立体形状，分子在哪里结合，哪里不结合，还有它所经之处造成的影响。

So, how do you know if a food has trans fat in it?

那么，你怎么知道一种食物是否还有反式脂肪呢？

Well, the only sure way to know is if you see the words, "partially hydrogenated" in the ingredients list.

唯一能够确定的方法是看食品成分里面有没有“部分氢化”的字眼。

Don't let nutrition labels or advertising fool you.

别让营养标签或广告骗了你。

The FDA allows manufacturers to claim that their products contain "0" grams of trans fat even if they actually have up to half a gram per serving.

美国食品药物管理局 (FDA) 允许制造商宣称他们的产品包含0克的反式脂肪，即使“每份”的反式脂肪含量多达 0.5 克（低于0.5克）。

But there are no hard and fast rules about how small a serving can be, and, that means, you'll have to rely on seeing those key words,

但是没有严格的规定限制“每份”最少应该是多少，这就意味着，你得依赖关键字——

partially hydrogenated, because that's how trans fats are made, by partially hydrogenating unsaturated fats.

部分氢化，因为那是制造反式脂肪的方式，即透过部份氢化不饱和脂肪。

So, let's go back to our olive oil and pancake mix from before.

那我们再回到我们之前提到的橄榄油和煎饼。

Olive oil is 100% fat.

橄榄油是 100% 的脂肪，

Pancake mix is only 11% fat.

煎饼只有约11%的脂肪。

But olive oil is mostly unsaturated fat, and it has no trans fat at all.

但是橄榄油含得大部分式不饱和脂肪，完全不含反式脂肪。

On the other hand, more than half the fat in pancake mix is either saturated or trans fat.

然而，煎饼里面超过一半的脂肪是饱和脂肪或反式脂肪。

And, so, even though olive oil has 10 times as much fat as pancake mix, it's healthy for you, whereas pancake mix is not.

所以，虽然橄榄油含的脂肪是煎饼的10倍，它对你是有益的，而煎饼则不然。

Now, I'm not trying to pick on pancake mix.

当然我并不是要故意针对煎饼。

There are lots of foods with this type of fat profile.

有很多的食品含有这种类型的脂肪。

The point is this: It's not how much fat you eat, it's what kind of fat.

重点是：吃多少脂肪不重要，而是你吃了什么样的脂肪。

And what makes a particular fat healthy or unhealthy is its shape.

决定一种脂肪是否健康的关键是它的形状。