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Olive oil is 100% fat; there's nothing else in it.
橄欖油含有100%的脂肪，除此之外沒有別的。
Pancake mix, on the other hand, is only about 11% fat.
相反，煎餅只有約11%的脂肪。
And, yet, olive oil is good for you, and pancake mix is not.
然而，橄欖油對你的身體有益，煎餅則不然。
Why is that?
為什么會這樣呢？
As it turns out, 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.
原來，我們攝入的脂肪含量并不影響我們的體重、膽固醇，或得心臟病的機率，這些只跟我們攝入的脂肪種類有關。
But let's back up: What is fat?
不過我們先回過頭來看看：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, we would see that the stuff we call fat is actually made up of molecules called triglycerides, and they are not all alike.
如果我們把三文魚放大，它是一種富含脂肪的魚，忽略掉內臟和組織只看細胞的話，我們就會看到脂肪，它其實是是由一種叫做三酸甘油酯的分子組成的，而這些分子并不完全相似。
Here's one example. Those three carbons on the left, that's glycerol.
舉個例子。左邊的那三顆碳分子是甘油。
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，能夠把其它分子緊緊連在一起。
The three long chains on the right are called fatty acids, and it's subtle differences in the structures of these chains that determine whether a fat is, let's say, solid or liquid; whether or not it goes rancid quickly; and most importantly, how good or how bad it is for you.
右邊的那三條長鏈被稱為脂肪酸，這些分子鏈結構的微妙差別決定了脂肪種類。比如，它們是固體還是液體，是否會很快變質，最重要的是，對你是有益還是有害。
Let's take a look at some of these differences.
讓我們來看看這些差別。
One is length. Fatty acids can be short or long.
一方面是長度。脂肪酸可長可短。
Another more important difference is the type of bond between the carbon atoms.
另一個更重要的區別是連接碳原子的碳鍵類型。
Some fatty acids have only single bonds.
有些脂肪酸只有單鍵。
Others have both single and double bonds.
另外一些則同時擁有單鍵和雙鍵。
Fatty acids with only single bonds are called saturated, and those with one or more double bonds are called unsaturated.
只有單鍵的脂肪酸叫做飽和脂肪酸，有單個或多個雙鍵的脂肪酸則為不飽和脂肪酸。
Now, most unsaturated fats are good for you, while saturated fats are bad for you in excess.
大部分的不飽和脂肪酸對人體有益，而過多的飽和脂肪酸則是有害的。
For saturated fats, the story pretty much ends there but not for unsaturated fats.
就飽和脂肪酸而言，結果很簡單，但不飽和脂肪酸不同。
The double bonds in these molecules have a kind of weird property; they're rigid.
雙鍵在這些分子中有一個奇怪特性，它們有十分堅固的剛性結構。
So, that means there are two ways to arrange every double bond.
這意味著雙鍵排列有兩種。
The first is like this, where both hydrogens are on same side and both carbons are on the same side.
第一種就像這樣，兩顆氫都在同一邊，兩顆碳也在同一邊。
The second way is like this.
第二種方式像這樣。
Now the hydrogens and carbons are on opposite sides of the double bond.
氫和碳在雙鍵對立的兩端。
