Nutrition Column: Trans Fat: a Hidden Dietary Demon?

Nutrition labels provide a lot of information on the types of fat found in foods. However, such labels currently don’t provide information on trans fats, one of the most damaging fats for arteries. That may change this year as the Food and Drug Administration moves to require that manufacturers add the grams of trans fats in their products to the Nutrition Facts label.

What are trans fats and why are they added to food? Trans fats are formed during a process in which vegetable oils are heated and exposed to hydrogen gas. This process, called hydrogenation, changes the structure of the fat in some places along its carbon backbone. The added hydrogen exerts a slight pull that rotates the fat chain, changing the configuration from what in chemistry is called "cis" to "trans." Thus, the name "trans fats." The process is done to improve the texture and keeping quality of oil-based fats.

Why are trans fats bad? Unlike unaltered polyunsaturated and monounsaturated fats, which do not adversely affect blood cholesterol, trans fats act like saturated fats by raising both total and LDL ("bad") cholesterol. In addition, trans fats lower HDL ("good") cholesterol, making them worse for the body than saturated fat. Trans fats also appear to boost blood triglyceride levels and impair the ability of blood vessels to dilate, both of which increase the risk for heart disease. Because of this, the Institute of Medicine of the National Academy of Sciences recently recommended that "trans fat consumption be as low as possible while consuming a nutritionally adequate diet." Americans currently consume around 5 grams of trans fats per day. This may not sound like much, but the Institute of Medicine would like to see the level closer to zero.

Trans fats in the diet. Although a few foods, including beef, pork, lamb, butter and milk, naturally contain small amounts of trans fats, most of the trans fat in our diet comes from partially hydrogenated vegetable oils. Common sources of partially hydrogenated vegetable oils include stick margarines, cakes, cookies, pastries and fried snack foods like crackers, potato chips and corn chips. Until food manufacturers are required to list trans fats on nutrition labels, the words "hydrogenated or "partially hydrogenated" in the ingredient list are a good indication that the product contains trans fats.

Margarine vs. butter. Always up for debate is whether choosing butter or margarine is healthier. Although margarines tend to contain more trans fat than butter, the total amount of trans and saturated fat found in most margarines is less than that found in butter. In addition to containing a large amount of saturated fat, butter also contains cholesterol. Therefore, most researchers still prefer margarines, particularly soft tub margarines that list a liquid oil as the first ingredient.