What Exactly Are Saturated, Unsaturated, Trans, and Omega-3 Fats?
Whenever I am in the fat and grease aisle of my local supermarket trying to decide which brand of ultra-processed industrial fat flakes would kill me off the quickest, I’m always confused by the labels. Which one again will clog my arteries as effectively as injecting bacon grease into my forearm? It wasn’t the unsaturated one, was it? And what are all these different types of fat anyway?
I would have thought there are just two types of fat: the jiggly one that grows under my skin and the oily one that grows on it. But no, it’s not that simple. There’s a whole slew of fatty substances we commonly consume with our doughnuts, sausages, avocados, peanuts, anchovies, and ice cream: saturated fat, unsaturated fat, monounsaturated fat, polyunsaturated fat, partially hydrogenated fat, trans fat, and at least three different kinds of omega fats. Some of them are said to be good for you and others are said to be good only for cardiologists and undertakers.
So, since I know that the food industry relies on my ignorance to sell me ultra-processed plastic-wrapped crap, I decided it was finally time to level up my knowledge about nutrition and take a look at fat. And after a few hours of study, I learned that slapping one’s love handles while standing in front of a mirror isn’t the way to go. I therefore decided to continue researching the topic by delving into the literature instead and this is what I found.
What is fat?
Fat is the stuff around your waistline, it’s the stuff you sit on, it’s the stuff that makes your fingers slippery and greasy when you eat french fries, and it’s the stuff that makes an elephant seal all wobbly. But to understand what saturated, unsaturated, and the other types of fat are, we have to take a much closer look at it — we have to look at fat at the molecular level. So let’s slide a piece of bacon or a slice of cheesecake under a microscope and see.
As you’ll probably remember from your high school chemistry, a molecule is just a bunch of atoms holding hands. For instance, water is a type of molecule made out of two hydrogen (H) atoms and one oxygen (O) atom, which I like to draw like this:
Now, chemists tend to think that a diagram like the one above is ridiculous and so they rather draw it with boring letters:
Either way, you can clearly see that water is made out of two hydrogens and one oxygen atom and that’s why it’s called H2O.
Fat, in much the same way, is a molecule too. Unlike water, however, it not only contains hydrogen and oxygen, but also lots of carbon (C) atoms. A fat molecule — or triglyceride if you want to use the fancy chemistry term — is therefore a whole lot of hydrogen and carbon atoms holding hands, with a few oxygen atoms thrown in. Here, this is how such a molecule looks like:
Yeah, I know. Scary. But let’s be bold and tackle this contraption. It’s actually not that hard to understand. It’s just a clothesline with three things hanging from it.
First, there’s the clothesline or backbone of the fat molecule:
This part is called a glycerol and for the purpose of distinguishing the different types of fat we don’t really care too much about its internals.
And then there’s the remainder of the molecule, which are simply three tails that are hanging from the glycerol clothesline:
These tails are called fatty acids and they are were all the differences between the different kinds of fat are actually found.
A closer look at fatty acids
Still scared? I hope not! Because to understand the difference between a saturated and an unsaturated fat, as well as the subtleties of trans and omega fats, we’ll now have to take an even closer look at that spooky fat. So, are you ready? Yes? Great!
Here, this is the molecular structure of the fatty acids:
As you can see, a fatty acid is basically a conga line of red carbon atoms surrounded by a whole lot of green hydrogen atoms and one blue oxygen atom at one end. Each carbon atom has four hands and it uses these hands to hold onto the other atoms that surround it.
Specifically, the first carbon atom in each of the three conga lines uses one hand (1 in the figure below) to hold onto the glycerol clothesline, two hands (2 and 3) to hold onto an oxygen atom, and the fourth hand (4) to hold onto the second carbon atom of the conga line:
Any carbon in the middle of the conga line, in turn, uses two hands (1 and 3 below) to hold onto neighboring carbon atoms and another two hands (2 and 4) to hold onto a hydrogen atom above and below it:
Finally, the last carbon atom (called the omega end) holds onto one carbon atom (1 in the figure below) and three hydrogens (2, 3, and 4):
With this, we have the basics out of the way and we can now look at some nuances that distinguish the different types of fat.
Who’s got the biggest?
As with noses, one way we can distinguish fatty acids from one another is by how long they are. For instance, they may be short, like in the picture below:
Or they may be long, like the second fatty acid you can see here:
Or they may be really long, like this pinocchio of a fatty acid:
Depending on the length, scientists refer to these fatty acids as short-chain, medium-chain, long-chain, or very long chain fatty acids — although if it had been up to me, I would have called them ding, dong, shlong, and ubershlong.
Now, although I think it would make great marketing, you’ve probably never seen a box of cookies announce how well-endowed its fatty acids are. But you can still figure out the length of the carbon chains indirectly by checking the type of fat or oil contained in the product. For instance, if the cookies contain palm oil, this tells you that they predominantly contain palmitic acid, which is a fatty acid with a 16-carbon long conga line. If, on the other hand, the cookies contain, let’s say, olive oil, this tells you that they mainly contain oleic acid, which is an 18-carbon long fatty acid.
What are saturated and unsaturated fats?
Saturated and unsaturated? You’ve most definitely seen that on food labels, haven’t you? So what do they mean?
Well, as it turns out, saturated and unsaturated refers to the number of hydrogens in the fatty acid tails. Specifically, if a fat molecule contains only fatty acids like the one below, which is as jam-packed with hydrogens as it can possibly be, then we call the fat containing them a saturated fat.
In other words, a saturated fat is a fat molecule whose three fatty acid chains are so chock-full — or saturated — with hydrogen that there’s no room for any more hydrogen:
An unsaturated fat, on the other hand, is one that contains at least one fatty acid that has a few hydrogens missing:
As a result, an unsaturated fat is one where, in principle, we could fit some more hydrogen in:
So what’s the deal with these hydrogens? Why do we care about the number of hydrogens in the fats we consume? Well, the answer is that having less hydrogens changes the physical properties of a fat.
Specifically, when a fat is saturated, it’s fatty acids are nice and straight:
Whereas if they lack a few hydrogens, then they end up with a kink in the unsaturated fatty acid:
This is so because when there are hydrogens missing, this leaves a few of the carbon atoms with a free hand:
But carbon atoms hate it when their hands are free. They don’t know what to do with them. So, when hydrogens are missing, instead of having their hands idle, they use them to form double bonds:
But these double bonds create a tighter hug between carbon atoms and they thus form a sort of stiff spot within the molecule that bends the fatty acid out of shape. As a result, unsaturated fat molecules have a kink and this kink changes one important physical property of the fat — it stops being a solid and becomes a liquid:
The reason for this is that when fats are saturated and straight, they can be tightly packed. But when they have a kink, they can no longer be packed as tightly and thus the fat turns liquid. It’s like the difference between trying to build a wall out of bricks and trying to build one out of misshapen potatoes. The former is stable and much more solid than the latter.
This is also why fats that come from animal sources — such as lard, tallow, butter, and bacon — tend to be solid or semi-solid at room temperature. After all, animal fats are generally saturated fats. They’re made out of bricks. Fats that come from vegetable sources — such as olive oil, sunflower oil, and other vegetable oils — on the other hand, tend to be liquid. They are unsaturated fats that have at least one kink in them and thus can’t really be stacked in any orderly way.
This lack of kinks in saturated fats, by the way, also explains to some degree why they are more likely to clog up your arteries: due to their shape they simply have a greater tendency to form a compact mass in your blood vessels.
Finally, lest you think I forgot telling you about the difference between monounsaturated and polyunsaturated fats, it’s this. If there is just one double bond (or kink) in a fat molecule, we say the fat is a monounsaturated fat:
Whereas if there are two or more double bonds (or kinks), we talk of a polyunsaturated fat:
What are trans fats?
Generally, fats from vegetable sources are much cheaper than fats from animal sources. So the food industry prefers to use vegetable sources in their junk food whenever they can. The problem, however, is that vegetable fats tend to be liquid at room temperature even though what’s often needed is something with the texture of butter.
Just think of microwave popcorn, cakes, and crackers. You wouldn’t want any of that to be swimming in oil, would you? So, in an effort to produce cheap cookies, doughnuts, and other snacks, Big Food has asked itself a question: can’t we straighten out the kinks in unsaturated vegetable fats to make them more solid? And the answer is yes! It’s possible. And it’s done through a process called hydrogenation.
So what’s hydrogenation? Well, as the word itself hints at, it’s the process of adding hydrogen to fatty acids. It works like this.
We start with an unsaturated fat — or oil to be precise — that has a couple of double bonds and is thus missing some hydrogens:
Then we proceed to straighten out the kinks in the fatty acid by taking a big tank full of hydrogen gas, taking aim, and bombarding the fatty acid with hydrogen pairs:
And boom! When we hit the fatty acid at just the right spot, the hydrogens get stuck and the double bond is broken up into a single bond, which leads to the kink being straightened out. Of course the actual process is a bit more complex, involving catalysts, sparging, and complex chemical reactions (a.k.a. magic), but the important point is that the process adds hydrogen, removes double bonds and kinks, and solidifies the liquid oil.
Now, if we inject as many hydrogens as possible, we’re doing full hydrogenation and as a result we obtain a fully-hydrogenated oil, which is the same as a saturated fat. But this often makes a vegetable oil too solid. It gives it a waxy texture instead of a creamy buttery one. So the food industry prefers to only inject a few hydrogens. This is called partial hydrogenation and the resulting fats are called partially-hydrogenated oils. You may have encountered them on food labels in the past, but hopefully you haven’t seen them in a while. Why? Because partially-hydrogenated oils are no longer considered safe for human consumption!
You see, partially-hydrogenated oils have a big problem. They not only straighten out kinks in the fatty acids through the addition of hydrogen and breaking of double bonds, but they also sort of twist the fatty acids around:
This twisting further straightens the fatty acid, but it’s “weird”. It turns normal double bonds (called cis double bonds) into unnaturally twisted double bonds (technically called trans double bonds), with any fat that contains such twisted fatty acids being called a trans fat.
Now, why exactly such twisted industrial trans fats are bad for you is still largely a mystery. But there is no doubt that they are. Plenty of epidemiological studies have shown a strong link between their consumption and cardiovascular diseases and many countries have enacted laws to ban them. The best information I could find about how they harm you is a recent study from 2020, which points to trans fats being so heart-chockingly bad because they cause inflammation, significantly raise LDL cholesterol (i.e., the bad cholesterol), and make your liver obese instead of just your butt and paunch.
What are omega fats?
Okay, time to deal with the last type of fat — the omega fats.
The one you’ve probably heard the most of is omega-3, which is mostly found in some types of fatty fish, like sardines, anchovies, and salmon, but also in shellfish like mussels. Moreover, you can find omega-3 fats in the supplement aisle of many grocery stores and health stores since there’s been a lot of hype surrounding their health benefits — even though taking them as supplements doesn’t seem to be doing much to prevent diseases according to systematic reviews. But I’m not here to sell you some snake or fish oil anyway. I’m simply here to tell you what omega fats are. So, what are they?
Well, it’s pretty simple. Omega fats are fats that contain polyunsaturated fatty acids, that is, fatty acids that have two or more double bonds — and thus kinks — in it. Specifically, they are fatty acids whose first double bond is a certain distance away from the tail end — which is also known as the omega end. For instance, omega-3 fatty acids are nothing more than fatty acids that have their first double bond after three carbon-to-carbon hops starting from the end:
Likewise, omega-6 fatty acids are nothing but fatty acids that have their first double bond after six carbon-to-carbon hops:
And omega-9 fatty acids are those where you’d have to hop nine times before you reach the first double bond.
As to the big deal with omega-3 fatty acids, it’s this: Western diets tend to be defficient in them even though they’re essential — meaning we have to ingest them because our bodies can’t make them — whereas omega-6 fatty acids are plentiful in our diets and omega-9 is non-essential.
So there you have it. If you paid any attention at all, you now know exactly what all these fat-related chemistry terms on food packaging and nutrition labels mean. And if you didn’t pay attention, well, I hope you’ll remember at least one thing: trans fats are really bad for you.
Now, please excuse me while I do some further research into fat...
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