We don’t talk a lot about dietary science
here on SciShow because, frankly, it can seem like a hype factory designed more to generate
clicks 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. 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. 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. 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: 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. 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. 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...so we literally
need to eat those kinds of fats in order to survive. 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! 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. 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. Thanks for watching this episode of SciShow,
which was brought to you by our patrons on Patreon. If you want to help support this show, just
go to patreon.com/scishow. 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.
