Yesterday, the FDA officially began steps to ban trans fats in the United States. Their ruling was that partially hydrogenated oils, the main source of dietary trans fats, are no longer “generally recognized as safe.” This suggests that the FDA intends to re-classify artificial trans fats as “food additives”. Because the burden will then shift to the company to demonstrate safety (a virtual impossibility given their well-documented dangers), this would result in what would essentially be an elimination of artificial trans fats from the American diet.

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 ScienceĀ 

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.

A triglyceride

Carbon has four valence electrons that want to find someone to love. Thus, carbon molecules need to form four bonds in order to be stable. In a fatty acid, those carbons form a lovely, long chain connecting carbon to carbon. Hydrogen molecules (which only need one bond to be happy) ensure that the carbon molecules all have four bonds.

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 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 transformation.

These simple facts open up three broad classes of fatty acids:

  1. 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.
  2. Fatty acids can have cis-formation double bonds. These are usually referred to as unsaturated fats. (Technically, trans fats are also unsaturated.)
  3. Fatty acids can have trans-formation double bonds. These are called trans fats.

Despite what you may have heard, unsaturated fats, saturated fats, and trans fats all occur naturally to some extent. However, saturated fats are frequently man-made and trans fats are almost always man-made.

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 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.

And who wants to live in a world without pie?

Saturated fats can be produced by a process called hydrogenation. This is literally exactly what it sounds like: You add hydrogens (plus a catalyst) to reduce the number of double of bonds. If you like, though, you don’t have to do the whole thing. By controlling the amount of hydrogen, the catalyst, or the temperature of the reaction, you can do a halfway job called “partial hydrogenation”. A company might choose partial hydrogenation if they want an end-product that is soft and malleable, like Crisco, instead of a solid, hard block of fat.

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)”.

The News

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 significant 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.

The FDA has opened a 60-day comment period to investigate the best way to phase out partially hydrogenated oils completely. From those comments, they will determine a timeline. New York City and California have both already banned trans fats from restaurants. Outside of the US, Denmark and Switzerland also have bans.

(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 eliminating 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.


1. This is amazing! Thanks for explaining it so well!

2. Glad to be of service! Most of the articles I saw didn’t actually bother explaining what trans fats actually are, and I figured that I should remedy that.

3. lalalalalalala, I can’t hear a thing you said about diet ice cream, lalalalalala. But the rest, as always, was fascinating.

4. Makeup and skincare aren’t magic and food isn’t magic either, haha.

5. What is your opinion on virgin (non partially hydrogenized) coconut oil? There seem to be a lot of conflicting opinions on this.

6. I cannot express my absolute LOVE for this post!!! Prior to deciding on neuroscience as my educational path, I seriously considered nutrition (mainly child and pre-natal nutrition). I have a similar diet philosophy as you – everything in moderation (within reason) with trans fats as one of my only exceptions. Again, I love love love this post. I was actually considering emailing you suggestions outside of cosmetics (GMOs, trans fats, and MSG) so I’m happy that further digging into your blog yielded this post!