So then what, in technical terms, is a trans fat — really? And in what way is it different from other, more common fats? To answer this question, we must return to that “E”-shaped triglyceride molecule I mentioned last week. As you’ll recall, triglycerides are “E”-shaped because they’re composed of a molecule of glycerol with three fatty acid molecules attached. Fatty acids come in many, many different kinds. You even get different types of fatty acids on the same triglyceride molecule, but for purposes of explanation, I’m going to assume that they’re all the same.
So then, you remember what I wrote about hydrogenation, the process by which hydrogen atoms are added to a fatty acid (hydrocarbon) chain. Here’s a convenient and “after” and “before” visual aid. Notice in the unsaturated example that when a carbon atom in the chain isn’t bonded to two hydrogen atoms, it uses its available bonds to double-bond to the carbon atom next to it. Carbon atoms are like that, they hate loose ends.
Follow me? Good. Now, suppose you get an instance where there are only two hydrogen atoms missing in a chain, but the vacancies are right next to each other. Carbon atoms being what they are, they’ll use their available bonds to hold on to one another in a double bond. That double bond puts a kink in the chain, like this. It’s this kink that would make this particular fat a liquid, since it’s odd shape would prevent it from being easily “stackable”, and as you may recall from other posts on crystallization, it’s this stacking action that creates crystals, and crystals create solidity.
Still with me? Excellent. Now here’s the critical bit. These types of double-bonded carbon atom configurations come in two types, “cis” and “trans”. If both of the hydrogen atoms in the bond are on the same side of the hydrocarbon chain, as in the previous “kinked molecule” example, it’s a “cis” which is Latin for, you guessed it, “on the same side”. If the two hydrogen molecules are on opposite sides of the chain, then you get a “trans” bond which means — anyone? anyone? — that’s right, “across”.
What’s the difference between the two bonds? Not that much, save for the fact that, as you saw, the trans bond straightens the fatty acid molecule back out again. The result is a fat molecule that stacks, which means it crystallizes, which means a fat composed of it solidifies. Pretty easy, no? Actually not so much, which is why very few of the people who talk so loudly about trans fats actually know what they are.