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Elaidic acid, the major trans fat found in hydrogenated vegetable oils


There is good reason to limit trans fats in the diet, good enough reason that many countries have passed legislation to restrict trans fats in products and restaurants. The good reason is that dietary trans fats increase the risk of coronary artery disease and heart attacks. But there is also a bogus reason to avoid trans fats: the myth that trans fats are metabolized very slowly and have a half-life of 51 days.

In the book Dr. Bob’s Trans Fat Guide: Why No Fat, Low Fat, Trans Fat is Killing You, he explains:

Do you remember in science class when your teacher talked about Madame Curie’s discovery of the half-life of uranium? Well, trans fat has a half life as well. Through research and experience, I have learned that the half-life of trans fat is fifty-one days. That may or may not seem like a lot, but understand how half-life works. When you eat a bag of chips, a deep friend doughnut, cream-filled cookies or anything with hydrogenated fat, it takes your body 51 days to properly metabolize and eliminate HALF of it. In another 51 days, HALF of that, 25 percent, is still in your body. That’s 102 days, over 3 months, and you still haven’t processed all of the trans fat you just ate!! If you are eating trans fat every day – and you are if you eat snack foods, prepackaged foods and deep fried foods – imagine how much trans fat is congesting your body from years of this eating pattern. That’s a pretty nauseating thought. Take two breaths and read this again.

In the following paragraph, he proceeds to blame trans fats for ADHD, depression, and Alzheimer’s; and claims what people are eating is slowly killing them.

Another alarmist cites the half-life as 52 days and claims that the process used to create trans fats causes your body to view them as a foreign substance, not food.

Simply not true

Those claims are simply not true. The terms trans and cis refer to stereoisomers, different geometrical configurations of molecules with the same chemical formula. Cis means that the functional groups are on the same side of the carbon chain; trans means they are on opposite sides. Trans fats are produced commercially by the process of hydrogenation, but they are also found in animal products. The body can’t tell whether the molecule came from an animal or a factory. The idea that trans fats in processed foods are viewed by the body as foreign substances is ridiculous. The metabolism of trans and cis fatty acids is the same. The concept of half-life doesn’t apply to their metabolism. So where did the 51-day myth originate?

Dr. Bob said so

The 51-day story apparently was invented by Dr. Bob, the author of the book quoted above.

Who is Dr. Bob? Dr. Bob DeMaria is a chiropractor who calls himself the drugless doctor. He’s against drugs, but is very much in favor of dietary supplements, which he sells. He has written about how he came up with the 51-day story: “…through my research and experience…” He doesn’t offer any supporting references. I can’t help but wonder what he thinks “research” means, and how his “experience” came up with the 51-day figure.

This 51-day half-life claim has been disseminated widely on numerous chiropractic and other alternative medicine websites. Amazingly, no one seems to have challenged this absurd assertion. So I will be the first to say it is absolute nonsense.

Conclusion: trans fats don’t have a 51-day half-life

As Christopher Hitchens said, “What can be asserted without evidence can be dismissed without evidence“. This claim can be dismissed.

Of course, it is still a good idea to limit trans fats in the diet – for real reasons, not imaginary ones.

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Posted by Harriet Hall

Harriet Hall, MD also known as The SkepDoc, is a retired family physician who writes about pseudoscience and questionable medical practices. She received her BA and MD from the University of Washington, did her internship in the Air Force (the second female ever to do so),  and was the first female graduate of the Air Force family practice residency at Eglin Air Force Base. During a long career as an Air Force physician, she held various positions from flight surgeon to DBMS (Director of Base Medical Services) and did everything from delivering babies to taking the controls of a B-52. She retired with the rank of Colonel.  In 2008 she published her memoirs, Women Aren't Supposed to Fly.