Trans Fats Explained

It'S A Hot Topic But Many Of Us Still Don'T Quite Get It

Robert L. Wolke
3 min read
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Q: I’m confused about trans fats. I recently read that hydrogenated and partially hydrogenated oils are considered trans fats. What is hydrogenation, and what does “partially” add to the picture?

A: In light of recent developments, there has been a strong resurgence of interest and confusion surrounding trans fatty acids, or “trans fats.”

Last July, the Food and Drug Administration issued its final rule on the labeling of foods containing trans fatty acids, to wit: “In this final rule and given the current state of scientific knowledge, FDA is requiring the mandatory declaration in the nutrition label of the amount of trans fatty acids present in foods. …” (Note that this new labeling is both “required” and “mandatory.” I wouldn’t be surprised if it were also compulsory and obligatory.) The rule is to become effective Jan. 1, 2006.

It’s not my bag to go into the health consequences of ingesting trans fatty acids. Suffice it to say that trans fatty acids are b-a-a-a-d. They raise your total blood cholesterol level and your LDL, or bad cholesterol, and lower your HDL, or good cholesterol. They are formed during hydrogenation.

Hydrogenation is a process in which hydrogen gas is forced into liquid, unsaturated fats such as soybean oil to make them semisolid and more serviceable as margarines or in food manufacturing. If they were hydrogenated completely, they would become as hard and inedible as candle wax. That’s why liquid vegetable oils are only partially hydrogenated.

Now here’s the problem. During hydrogenation, the added hydrogen atoms can settle into the fat molecules in either of two different ways that chemists call cis (pronounced sis) and trans. Almost all fatty acids in nature are in the cis form, but hydrogenation produces the unnatural trans form also. They cause trouble in our bodies because their molecules are a different shape: kinky instead of relatively straight.

Until the FDA’s required, mandatory, compulsory and obligatory labeling takes effect, how can you tell where all the trans fatty acids are hiding?

Hydrogenated fats lurk in virtually everything you love to eat: commercial cakes and cookies, doughnuts, potato chips, crackers, popcorn, nondairy creamers, whipped toppings, margarine, gravy mixes, cake mixes, frozen French fries and pizzas, fish sticks and virtually all fried foods, unless you fry them yourself in un-hydrogenated oils. But trans fatty acids are also formed by the high temperatures of frying, so you may be making them yourself. And to make things worse, restaurants that brag about using only “pure vegetable oil” don’t tell you that it’s probably been hydrogenated to within an inch of its life.

There is, however, a ray of hope. The amounts of trans fatty acids formed in the hydrogenation of oils depends on the temperature, hydrogen pressure, length of exposure and many other factors. Now that the pressure is on from the Feds, you can bet your Twinkie that packaged food manufacturers will accelerate their efforts to find ways of attaining the desired physical characteristics in their fats with minimum production of trans fatty acids. They want to earn the right to put the coveted phrase, “Contains no trans fatty acids,” or “Contains no trans fats,” on their labels.

Robert L. Wolke ( is professor emeritus of chemistry at the University of Pittsburgh and the author of What Einstein Told His Cook: Kitchen Science Explained.


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