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Trans fatty acids: What are they and why shouldn't you eat them?

American Chemical Society

Just what is the skinny on those trans fatty acids that are so bad for you? Donuts, stick margarines, French fries, cookies and other tasty snacks are loaded with them. And this summer the Food and Drug Administration decreed that as of Jan. 1, 2006, manufacturers must break the trans fats category out of the total fat listing on labels.

Chemical &Engineering News, in its Sept. 22 issue, describes the chemistry of these culprits. C&EN is the newsmagazine of the American Chemical Society, the world's largest scientific society.

In issuing its order, the FDA relied mainly on an Institute of Medicine report that concluded that consuming foods containing trans fatty acids raises LDL (bad) cholesterol and the risk of coronary heart disease, according to C&EN. The IOM recommended people keep their consumption of trans fats as low as possible, and to help consumers do this the FDA issued the labeling requirement.

What are trans fatty acids?

Unsaturated fats, found in such foods as avocados and olive and corn oils are heart healthy, but in the air they can go rancid by absorbing oxygen and then decompose, C&EN explains. Manufacturers can stop this process by bubbling hydrogen (hydrogenation) through the fat at a high temperature in the presence of a catalyst like nickel and in the absence of oxygen.

The process raises a fat's melting point, turning liquid vegetable oil into products ranging from soft margarine to solid shortening, according to the newsmagazine. When the healthful unsaturated fats are partially hydrogenated, the double bonds are rearranged, converting some to the trans configuration and shifting the double bonds along the chain. Unfortunately, this newly created trans fatty acid is an artery-clogger.

Amid the criticism of cookies, chips and other products containing trans fat, a number of companies have either developed foods without partially hydrogenated oils or have pledged to explore ways of replacing the fat. PepsiCo's Frito Lay, for example, has already eliminated trans fats from some of its products.

To access the C&EN article on trans fats, go to:


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