My food philosophy has always been an "everything in moderation" sort of strategy. Trans fats are my one exception, thanks to a particularly enthusiastic and competent chemistry teacher who taught me sophomore, junior, and senior year of high school.
The chemistry of fats is relatively simple. Fats are legally defined as triglycerides*. This means that they are three fatty acids linked together by a simple sugar called glycerol. The fatty acids are made up of a carboxyl group and a super long chain of carbon molecules called an aliphatic compound.
You can also satisfy a carbon's need for bonds with something called a double bond. Instead of sharing two electrons (like the carbon and hydrogen are are doing), they share four. Then, two of carbon's four valence electrons are occupied, so the carbon molecule only needs three bonds, which are locked in place by the double bond. That adds some new potential variation. The two hydrogen molecules can be on the same side, called the cis formation, or they can be on the opposite side, called the trans formation.
- Fatty acids can be completely filled up with hydrogen, with no double bonds at all. Since they are saturated with hydrogen, they are called saturated fats.
- Fatty acids can have cis-formation double bonds. These are usually referred to as unsaturated fats. (Technically, trans fats are also unsaturated.)
- Fatty acids can have trans-formation double bonds. These are called trans fats.
Unsaturated fats (the kind of fats you might find in, say, olive oil) contain less energy, meaning that they have fewer calories than their saturated counterparts. However, they have a few disadvantages. The most notable is that they are susceptible to a chemical process known as lipid peroxidation, in which free radicals steal the electrons in the fat's double bonds. This results in rancidity. If you manufacture Twinkies (or whatever), obviously this is a really big concern for you because you don't want your Twinkies to go bad.
The other big disadvantage of unsaturated fats is that they are liquid at room temperature. One of the big ways that molecules interact with each other is called Van der Waals force, which are super weak forces that operate outside of stronger forces such as bonds. Unsaturated molecules are are all wonky and they don't fit together. That means that there are fewer Van der Waals forces holding them together, and it's easy to pry them apart. Their melting temperature, then, is pretty low, meaning we usually encounter them in liquid form. Saturated fats, on the other hand, fit together perfectly. This means more Van der Waals forces acting on the molecules, meaning they are harder to rip apart and have a higher melting temperature. Thus, they're probably going to be solid at room temperature, like lard would be. If you don't understand why this is a problem, I dare you to try to make a pie crust out of olive oil.
Unprocessed fats are almost always in the cis configuration. However, since the trans configuration is lower energy than the natural cis formation, partial hydrogenation results primarily in trans fats. It's a byproduct that must be produced during partial hydrogenation. Since hydrogen molecules are added one at a time, partial hydrogenation will always give you a shitload of trans fats.
Trans fats (and saturated fats, of course) are processed differently than unsaturated fats, elevating cholesterol and triglyceride levels in the blood. Although the full mechanism is not yet known, it is clear that the liver plays a crucial role. For example, the PGC-1beta coactivator protein is triggered by trans fats, altering liver metabolism. This ultimately puts consumers at risk for heart disease, diabetes, and certain types of cancers. As the New England Journal of Medicine notes, "from a nutritional standpoint, the consumption of trans fatty acids results in considerable potential harm but no apparent benefit." Mozaffarian and colleagues add, "Trans fats appear to increase the risk of [coronary heart disease] more than any other macronutrient, conferring a substantially increased risk at low levels of consumption (1 to 3% of total energy intake)".
Outcries by public health advocates have led to substantial voluntary decreases in trans fats in the past few yeas (because people like me refuse to eat them). One of my elated thoughts after hearing this news was, "I can finally eat at Jack-In-the-Box again!" When I checked, though, it seems that they have actually been trans fat-free since 2010. (If they still made Chipotle Chicken Ciabattas, my unnecessary boycott would almost certainly qualify as a tragedy!) Presumably, this is related to FDA requirements to disclose trans fat content on product nutrition facts. However, trans fats are still quite common, especially in pre-made food. This constitutes a significantly public health hazard. According to the FDA, a ban on trans fats would prevent 20,000 heart attacks and 7,000 deaths from heart disease every single year.
(It's worth noting that the FDA is focusing exclusively on partially hydrogenated oils. Some trans fats are found in other food products. For example, they are byproducts in the manufacture of fully hydrogenated oils. There are also naturally-occurring trans fats, such as vaccenic acid. Those of you who know your Latin may have already inferred the source of this fatty acid: beef and dairy products. However, naturally occurring fatty acids like vaccenic acid have not been associated with the negative health effects of partially hydrogenated oils and may even be somewhat beneficial.)
There are definitely a few potential pitfalls in this new decision. Most notably, some processed food will probably have a slightly shortened shelf life and may increase in price. This will be especially problematic for Americans who are living in poverty, and it is important that governmental assistance programs made adjustments as needed. Additionally, many products, ranging from coffee creamer to Bisquick, will require substantial re-formulations, which may affect their flavor. (With that said, I do want to explicitly state that trans fats do not taste better. That's a myth I see getting thrown around a lot... my mom is particularly convinced that reducing trans fats will result in less appealing food. It won't! In fact, pure fat tastes like nothing at all. Impurities in yours oils are what give them different flavors, and it's only the texture that poses a meaningful concern!)
Overall, I believed that the FDA's step to eliminate artificial trans fats is a fabulous one. Hooray for public health!
*Note that I am talking about the legal definition, not the practical one. It is common practice for diet food products to chemically split triglycerides into mono- and diglycerides so that they can say that they contain less fat. Since the very first step of triglyceride metabolism is to split the fatty acids into mono- and diglycerides, your body is still treating these molecules as fat, even if the label doesn't. Fuck you, diet ice cream.