If you’re an avid ketogenic diet follower, then you are likely embracing all the fatty foods that come with the territory of low-carb life. However, all fats are not made equal, especially trans fat. 

Many fitness aficionados are well aware of the health risks that synthetic trans fat can bring about. (If you’re not up to speed on this we will touch on it later). Moreover, many people may be misinterpreting food labels when they see the term “hydrogenated oil” listed in the ingredients.

It’s important to note that some trans fat is found in natural food products – like cheese and butter – often in the form of conjugated linoleic acid (CLA). Natural trans fat, like CLA, actually appears to be healthy and may even enhance weight loss on the keto diet. (This is why we recommend butter/ghee for keto-friendly foods).

This article is going to focus on synthetic trans fat – which is formed from the chemical process known as ‘partial hydrogenation‘; this process converts a liquid fat/oil into semi-solid fat at room temperature (things like margarine, shortening, etc). However, the keyword that people may be skipping over is ‘partial.’

Read on as we take a closer look at why ‘fully’ and ‘partially’ hydrogenated fats are not the same and why the former isn’t always a bad thing.

Chemical Hydrogenation of Fats

If you’re somewhat up to speed on chemistry lingo, you’ve likely derived the meaning of hydrogenation already. Hydrogenation is simply the addition of hydrogen atoms to a molecule. The chemical reaction is generally carried out with:

  • molecular hydrogen (diatomic hydrogen/H2)
  • heat
  • a metal catalyst such as nickel or platinum

Fatty acids are chains of hydrocarbons, which means they are composed purely of carbon and hydrogen atoms. Therefore, unsaturated fats (like liquid vegetable oils), are fatty acids that contain one (mono) or more (poly) carbon-carbon double bond (due to missing a hydrogen atom in the hydrocarbon chain).

Chemical hydrogenation is the process that converts these unsaturated fats into saturated fatty acids (which do not contain carbon-carbon double bonds since the carbons are “saturated” with hydrogen atoms). For a more visual representation of this process, see the image below.

Trivia time: Why is this not a “full” hydrogenation? (the answer is below, don’t peek, cheater!)

Trivia Answer: If this were a complete/full hydrogenation process, there would be NO double bonds remaining in the final triglyceride component.

Difference between Cis/Trans Fat & Partial/Full Hydrogenation

Now you have a rudimentary understanding of what happens at the molecular level during chemical hydrogenation. Let’s take a look at the two different forms of fats that may be made by this process.

In the instance of partial hydrogenation (depicted above), the final triglyceride product still contains unsaturated fats, and in the reaction above the final product contains “cis” fatty acids (which means the carbon chain extends from the same side of the double bond).

A “trans” fatty acid, on the other hand, has a carbon chain extending from the opposite side of the double bond. For a visual schematic of these two types of unsaturated fatty acids see the image below.

As you can see, the trans isomer of oleic acid remains a rather straight molecule; the cis isomer has a “kink” in it and bends.

This difference in the chemical structure of unsaturated fatty acids is the basis to their ramifications in human health. (Your body metabolizes them differently.)

If you’ve been able to keep up with this so far, you’re likely ahead of the game and already know why fully hydrogenated fats are not always necessarily “bad” fats.

Again, the reaction we looked at earlier was a partial hydrogenation of a typical vegetable oil. In other words, a few double bonds remain in the final product. 

Therefore, the complete/full hydrogenation process leaves no double bonds in the final product, thus converting an unsaturated fat to a saturated fat.

“Which is ‘worse’ for health purposes, complete or partial hydrogenation?”

I hope by this point I haven’t lost too many readers in the details. The main thing I want you to take away from this is that chemical hydrogenation doesn’t always create trans fat.

The good news is that most countries are moving away from the use of partial hydrogenation for domestic food. Nevertheless, be wary of synthetic trans fat in the food you eat; intake of these fats should be minimal/trivial (if any at all).

On the other hand, full hydrogenation creates saturated fats, which are a necessary component of the human diet. However, don’t take this to mean that you should start incorporating tons of margarine in your diet; rather, you can consume those foods in moderate amounts (but still keep an eye on your intake of them).

It’s still in your best interest to aim to take in the majority of your fats in the unsaturated form. You can find ample amounts of unsaturated fats in foods like nuts/nut butter, fish, flaxseed, olive oil, and others.