We don’t talk a lot about dietary science here on SciShow
因为 平心而论 这样科学秀就更像是早已安排好的工厂在宣传商品 而不是帮助大众形成认知
because, frankly, it can seem like a hype factory designed more to generate goods than to generate understanding.
People want to hear what to eat and what not to eat in order to be healthy.
The problem with that… is that it’s complicated.
It’s too complicated to fit into a headline.
Eating lots of fat will make you unhealthy, but so will eating lots of anything.
研究表明 当尝试帮助人们减肥时 减少脂肪摄入量是无用的
Studies show that cutting fat intake is useless when attempting to help people lose weight
if those calories are replaced by something else, which they tend to be.
如今 脂肪在化学上是相对明确的 但它却使饮食家 尤其是那些写了几十年的新闻工作者惶恐
Now fat is relatively straightforward chemically, but it’s boggled dietary scientists and, especially, journalists writing about it for decades.
But the basics of what we understand aren’t that complicated, so let’s get to the heart of fat.
Fats are molecules that organisms use to store energy…they are very good at that
and so they can be converted into lots and lots of energy for running an organism,
whether it’s a seed growing into a plant or a neuron firing in your brain.
Fat is super good at energy storage.
In nutrition, we talk about energy in “calories” which is really a measure of heat.
然而 根本上来说 要了解脂肪首先要了解它的能量密度
But, basically, the first thing to know about fat is that it is energy dense.
So per gram, fat has more than twice the energy of protein or carbohydrates.
Fats, like everything we eat, are made of chemicals.
And those chemicals are primarily composed of large chains of carbon atoms.
Each of those carbon carbon bonds can be broken by your body and converted into usable energy.
The energy density of fat combined with the fact that people who ate high fat diets tended to be less healthy
was the original cause of the anti-fat craze that started in the 60s and continues at least to some extent today.
But it turns out that fats are not inherently bad for you,
indeed, they are an absolutely necessary part of the diet.
But there are definitely some fats that promote health more than others, and some that are downright dangerous.
You’ve heard of the main categories:
反式 饱和 不饱和 氢化 多元不饱和 欧米加-3-……
You got your trans, saturated, unsaturated, hydrogenated, polyunsaturated, omega 3…
all of these words are chemistry terms that get talked about a lot without discussing what they mean, like, at all.
But this is SciShow, so let’s go there.
Carbon has four unpaired electrons, so each carbon atom likes to bond to four other things.
This is methane: carbon bonded to four hydrogens.
And yes, I am using snatoms– Veritasium’s molecular modeling kit which I’m very excited about.
If the carbon is in a saturated carbon chain, two of those things will be other carbons–
unless it’s the end of the chain.
And two of those things are going to be hydrogen.
If this is what the carbon chain looks like with a bunch of carbon atoms, each bonded to two carbons and two hydrogens
that is a saturated fat
which tend to be solid and are mostly made by animals…though also coconuts.
The thing that saturated fats are saturated with is hydrogen.
Every carbon is bonded to two of them, except the last, which is bonded to three.
And unsaturated fats are not saturated.
They have fewer hydrogens…how?
Well they’ve got at least one double bond between two carbons in the chain.
Each double bond means two fewer hydrogens.
So unsaturated fats don’t have as many hydrogens as they could have per carbon atom.
And this is not as minor a change as it might sound.
Single bonds can rotate around their axis no problem, but double bonds lock a structure into place.
And that double bond can either lock the chain into a kink or lock it straight.
In nature, a double bond in a fat chain almost always locks it into a kink.
This prevents the fat molecules from stacking into lattices making them more likely to be liquid at room temperature.
因此 不饱和脂肪往往是液态 也就是油 它们大多取自于植物和鱼类
So unsaturated fats tend to be liquid, making them oils, and come mostly from plants and fish.
The kinked configuration is called the “cis isomer” and the straight one is the trans isomer.
The word ‘isomer’ just means that the molecules have the same chemical formula,
but are different shapes.
And the different shapes matter…a lot.
Saturated fats are less healthy than unsaturated fats because they pack together easily and
can form plaques in your arteries and can also interact with cholesterol making it build up in your bloodstream.
Cis unsaturated fats (which the rest of the world just calls unsaturated fats) don’t stack well
and so don’t form plaques.
So that difference exists, but it isn’t as big as we used to think it was.
It turns out our bodies are pretty good at dealing with whatever we throw at it…
as long as it’s fairly familiar.
Worse by far are the trans unsaturated fats.
These are almost all manufactured by adding hydrogens or “partially hydrogenating” some unsaturated fat like soybean oil.
So trans fat and hydrogenated fats are the same thing…
one refers to the process through which they are created, the other their chemical structure.
These are fats that have double bonds AND stack well…in fact, they stack even better than saturated fats
AND our biochemical systems aren’t designed to break them down
AND they interact badly with cholesterol.
A two percent increase in daily intake of trans fat corresponds with a 23% increase in the chance of heart disease.
Amazingly they were initially seen as a healthy alternative to saturated fats
and are now in the process of being completely banned in America.
如今 即使在这些种类中有变种 在那变种中有
Now, even in these categories there’s variation, and inside that variation comes
more active areas of research where less is known for sure.
Polyunsaturated fats, or fats with more than one double bond might be more or less healthy than monounsaturated fats…
no one really agrees because they both have benefits and drawbacks,
and it matters where in the chain the double bonds are.
You should probably have some of both.
And If the double bond is just before the third carbon from the end,
we call that an omega three fatty acid and they seem to have a wide range of benefits.
And they’re also one of the two essential fatty acids (the other being omega 6).
Essential compounds are chemicals that our bodies need to function correctly but can’t manufacture on their own…
因此 为了生存 我们确实需要摄食那些脂肪
so we literally need to eat those kinds of fats in order to survive.
的确 一般而言 我们摄取脂肪是为了生存
And indeed, we need to eat fat in general to survive.
It’s good for you…in the correct quantities.
So those are the basics of fat you guys!
脂肪本身贮存了大量的能量 因此当你需能时 它们是很好的选择
They have TONS of energy in them, so they’re great when you need calories.
But they also make it super easy to eat too many calories.
它们对生命是必不可少的 尝起来也不错 对身体也好
They’re absolutely necessary for life, they taste good and are good for you,
but unsaturated fats are better and trans fats might very well kill you.
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And if you’re interested in Snatoms– I’m not sure if the kickstarter is still going on–
but they’re basically these little magnetic modeling kits.
They’re very cool, we’ll put a link in the description.