0:00:13.663,0:00:15.924
Olive oil is 100% fat;

0:00:15.924,0:00:16.964
there's nothing else in it.

0:00:16.964,0:00:18.232
Pancake mix, on the other hand,

0:00:18.232,0:00:20.489
is only about 11% fat.

0:00:20.489,0:00:22.761
And, yet, olive oil is good for you,

0:00:22.761,0:00:24.931
and pancake mix is not.

0:00:24.931,0:00:26.312
Why is that?

0:00:27.511,0:00:28.478
As it turns out,

0:00:28.478,0:00:29.889
the amount of fat we eat

0:00:29.889,0:00:30.931
doesn't impact our weight

0:00:30.931,0:00:31.858
or our cholesterol

0:00:31.858,0:00:33.064
or our risk of heart disease

0:00:33.064,0:00:35.924
nearly as much as what kind of fat we eat.

0:00:35.924,0:00:37.123
But let's back up:

0:00:37.123,0:00:39.347
What is fat?

0:00:39.347,0:00:40.925
If we were to zoom in on a salmon,

0:00:40.925,0:00:42.003
which is a fatty fish,

0:00:42.003,0:00:42.823
past the organs,

0:00:42.823,0:00:43.613
past the tissues,

0:00:43.613,0:00:45.329
into the cells,

0:00:45.329,0:00:47.421
we would see that the stuff we call fat

0:00:47.421,0:00:50.626
is actually made up of molecules called triglycerides,

0:00:50.626,0:00:52.545
and they are not all alike.

0:00:52.545,0:00:53.629
Here's one example.

0:00:53.629,0:00:55.730
Those three carbons on the left, that's glycerol.

0:00:55.730,0:00:57.262
Now, you can think of that as the backbone

0:00:57.262,0:00:59.635
that holds the rest of the molecule together.

0:00:59.635,0:01:00.929
The three long chains on the right

0:01:00.929,0:01:02.379
are called fatty acids,

0:01:02.379,0:01:05.273
and it's subtle differences in the structures of these chains

0:01:05.273,0:01:06.783
that determine whether a fat is,

0:01:06.783,0:01:08.938
let's say, solid or liquid;

0:01:08.938,0:01:11.143
whether or not it goes rancid quickly;

0:01:11.143,0:01:15.236
and, most importantly, how good or how bad it is for you.

0:01:15.236,0:01:17.024
Let's take a look at some of these differences.

0:01:17.024,0:01:18.075
One is length.

0:01:18.075,0:01:20.160
Fatty acids can be short or long.

0:01:20.160,0:01:21.414
Another, more important difference

0:01:21.414,0:01:24.280
is the type of bond between the carbon atoms.

0:01:24.280,0:01:26.914
Some fatty acids have only single bonds.

0:01:26.914,0:01:29.831
Others have both single and double bonds.

0:01:29.831,0:01:31.354
Fatty acids with only single bonds

0:01:31.354,0:01:32.834
are called saturated,

0:01:32.834,0:01:34.619
and those with one or more double bonds

0:01:34.619,0:01:36.667
are called unsaturated.

0:01:36.667,0:01:39.256
Now, most unsaturated fats are good for you,

0:01:39.256,0:01:42.090
while saturated fats are bad for you in excess.

0:01:42.090,0:01:44.713
For saturated fats, the story pretty much ends there

0:01:44.713,0:01:47.120
but not for unsaturated fats.

0:01:47.120,0:01:48.831
The double bonds in these molecules

0:01:48.831,0:01:50.515
have a kind of weird property;

0:01:50.515,0:01:52.139
they're rigid.

0:01:52.139,0:01:54.062
So, that means there are two ways

0:01:54.062,0:01:55.883
to arrange every double bond.

0:01:55.883,0:01:57.005
The first is like this,

0:01:57.005,0:01:58.902
where both hydrogens are on same side

0:01:58.902,0:02:00.824
and both carbons are on the same side.

0:02:00.824,0:02:02.648
The second way is like this.

0:02:02.648,0:02:04.193
Now the hydrogens and carbons

0:02:04.193,0:02:06.718
are on opposite sides of the double bond.

0:02:06.718,0:02:08.326
Now, even though both of these molecules

0:02:08.326,0:02:10.826
are made up of exactly the same building blocks,

0:02:10.826,0:02:13.329
they are two completely different substances,

0:02:13.329,0:02:16.468
and they behave completely differently inside of us.

0:02:16.468,0:02:18.972
The configuration on the left is called CIS,

0:02:18.972,0:02:20.376
which you've probably never heard of.

0:02:20.376,0:02:22.084
The one of the right is called TRANS,

0:02:22.084,0:02:24.713
and you probably have heard of trans fats before.

0:02:24.713,0:02:25.883
They don't go rancid,

0:02:25.883,0:02:27.843
they're more stable during deep frying,

0:02:27.843,0:02:29.817
and they can change the texture of foods

0:02:29.817,0:02:31.806
in ways that other fats just can't.

0:02:31.806,0:02:34.097
They're also terrible for your health,

0:02:34.097,0:02:35.974
by far worse than saturated fat,

0:02:35.974,0:02:38.019
even though technically they're a type

0:02:38.019,0:02:39.978
of unsaturated fat.

0:02:39.978,0:02:41.321
Now, I know that seems crazy,

0:02:41.321,0:02:42.517
but your body doesn't care

0:02:42.517,0:02:44.656
what a molecule looks like on paper.

0:02:44.656,0:02:46.575
All that matters is the 3-D shape

0:02:46.575,0:02:47.694
where the molecule fits,

0:02:47.694,0:02:48.406
where it doesn't,

0:02:48.406,0:02:50.990
and what pathways it interferes with.

0:02:50.990,0:02:51.950
So, how do you know if a food

0:02:51.950,0:02:53.827
has trans fat in it?

0:02:53.827,0:02:55.012
Well, the only sure way to know

0:02:55.012,0:02:56.084
is if you see the words,

0:02:56.084,0:02:59.255
"partially hydrogenated" in the ingredients list.

0:02:59.255,0:03:02.034
Don't let nutrition labels or advertising fool you.

0:03:02.034,0:03:04.090
The FDA allows manufacturers to claim

0:03:04.090,0:03:05.759
that their products contain

0:03:05.759,0:03:08.004
"0" grams of trans fat

0:03:08.004,0:03:12.635
even if they actually have up to half a gram per serving.

0:03:12.635,0:03:14.104
But there are no hard and fast rules

0:03:14.104,0:03:15.683
about how small a serving can be,

0:03:15.683,0:03:18.730
and, that means, you'll have to rely on seeing those key words,

0:03:18.730,0:03:20.005
partially hydrogenated,

0:03:20.005,0:03:22.858
because that's how trans fats are made,

0:03:22.858,0:03:25.776
by partially hydrogenating unsaturated fats.

0:03:25.776,0:03:28.967
So, let's go back to our olive oil and pancake mix from before.

0:03:28.967,0:03:31.609
Olive oil is 100% fat.

0:03:31.609,0:03:34.339
Pancake mix is only 11% fat.

0:03:34.339,0:03:37.205
But olive oil is mostly unsaturated fat,

0:03:37.205,0:03:39.840
and it has no trans fat at all.

0:03:39.840,0:03:42.001
On the other hand, more than half the fat

0:03:42.001,0:03:45.008
in pancake mix is either saturated or trans fat.

0:03:45.008,0:03:47.339
And, so, even though olive oil has 10 times

0:03:47.339,0:03:49.133
as much fat as pancake mix,

0:03:49.133,0:03:50.593
it's healthy for you,

0:03:50.593,0:03:52.386
whereas pancake mix is not.

0:03:52.386,0:03:54.180
Now, I'm not trying to pick on pancake mix.

0:03:54.180,0:03:55.264
There are lots of foods

0:03:55.264,0:03:57.183
with this type of fat profile.

0:03:57.183,0:03:58.409
The point is this:

0:03:58.409,0:04:00.103
It's not how much fat you eat,

0:04:00.103,0:04:01.795
it's what kind of fat.

0:04:01.795,0:04:04.610
And what makes a particular fat healthy or unhealthy

0:04:04.610,0:04:06.611
is its shape.