What's Wrong with Trans Fatty Acids

The New York City Board of Health has recently required that restaurants reduce the content of trans fatty acids so that each serving contains less than 0.5 grams. A recent study in the New England Journal of Medicine showed that a 2% increase in caloric intake from trans fatty acids was associated with a 23% increase in the incidence of coronary artery disease. The association is stronger with heart disease than it is with saturated fats.

What are trans fatty acids? Naturally occuring fats consist of saturated and unsaturated fatty acids. Unsaturated oils (vegetable oils) are converted to the trans form by partial hydrogenation to increase their stability and to raise the melting point. This process converts vegetable oils into semisolid fats for use in margarines, commercial cooking, and manufacturing processes.

Why are trans fatty acids bad for you? Previously it was assumed that trans fatty acids would be healthier than saturated fats, but they have been shown to decrease HDL cholesterol (the good cholesterol) and increase LDL cholesterol (the bad cholesterol). They also cause damage to the lining of blood vessels. In addition they have shown to promote abdominal fat depostion and insulin resistance both of which are early changes in the development of type 2 diabetes.

Where are trans fatty acids found? Deep fried food, packaged snacks, and bakery products are the major sources of trans fatty acids in the US. The average daily intake in the US is about 2.6 % or 6 grams in a typical 2000 calorie diet. The American Heart Association recommends limiting intake of trans fatty acids to 1% of daily caloric intake. Deep fried fast-food products may include 10 grams per serving.

How to avoid the bad fats? The American Heart Association recommends the following:

--Choose a diet rich in fruits, vegetables, whole-grain, high-fiber foods, and fat-free and low-fat dairy most often.
--Keep total fat intake between 25 and 35 percent of calories, with most fats coming from sources of monounsaturated and polyunsaturated fats such as fish, nuts, seeds and vegetable oils most often.
--Use naturally occurring, unhydrogenated vegetable oils such as canola, safflower, sunflower or olive oil most often.
--Look for processed foods made with unhydrogenated oil rather than partially hydrogenated or hydrogenated vegetable oils or saturated fat.
--Look for ”0 g trans fat” on the Nutrition Facts label.
--French fries, doughnuts, cookies, crackers, muffins, pies and cakes are examples of foods that are high in trans fat. Don't eat them often.
--Limit the saturated fat in your diet. If you don't eat a lot of saturated fat, you won't be consuming a lot of trans fat.
--Limit commercially fried foods and baked goods made with shortening or partially hydrogenated vegetable oils. Not only are these foods very high in fat, but that fat is also likely to be very hydrogenated, meaning a lot of trans fat.
--Commercial shortening and deep-frying fats will continue to be made by hydrogenation and will contain saturated fat and trans fat. That's just one more reason to eat fried fast food infrequently.

References: The Medical Letter, vol 49 (issue 1267), August 13, 2007. Please see above links.

Photo: courtesy of University of Pennsylvania Health Systems.