C&EN: SCIENCE & TECHNOLOGY - THE SKINNY ON TRANS FATTY ACIDS

SOPHIE WILKINSON

Donuts, cookies, stick margarine, french fries, and other tasty treats contain significant amounts of trans fatty acids. For now, food producers don't need to specify how much of these artery-clogging fats are present in their products. Instead, they are included in the "total fat" line on nutrition labels. But in July, the Food & Drug Administration decreed that as of Jan. 1, 2006, manufacturers must break the trans fats category out of the total fat listing.

FDA's action was prompted by the so-called food police, more formally known as the Center for Science in the Public Interest (CSPI), based in Washington, D.C. Back in 1994, this nonprofit health-advocacy organization filed a petition urging the agency to require producers to list the amount of trans fat on nutrition labels.

FDA gathered public comments and nutritional and health data as it considered CSPI's request. The agency relied particularly on a recent Institute of Medicine report on trans fats that concludes that "there is a positive linear trend between trans fatty acid intake and total and LDL [low-density lipoprotein] cholesterol concentration, and therefore increased risk of coronary heart disease. ... It is recommended that trans fatty acid consumption be as low as possible while consuming a nutritionally adequate diet."

Edible fats and oils consist almost entirely of fatty acids. Fats and oils of animal origin--such as butter and lard--are composed primarily of saturated fatty acids, which consist of a chain of methylene groups terminated by a carboxyl group at one end and a methyl group at the other. Palmitic acid is a common one. Health-promoting diets minimize saturated fat.

CHIPPER Frito-Lay proudly discloses that its Doritos are free of trans fats.
Photo by Sophie Wilkinson

Fats and oils derived from plants and some seafood consist mostly of monounsaturated and polyunsaturated fatty acids, which include, respectively, one or more double bonds between carbons in the chain. Oleic acid is an example.

Unsaturated fats, found in foods such as avocados and olive and corn oils, are heart-healthy, but they do have some undesirable properties. In air, unsaturated fatty acids can gradually go rancid by absorbing oxygen and forming hydroperoxides that decompose.

Manufacturers can block that deterioration and improve food texture by partially or fully hydrogenating the unsaturated fat. Hydrogen is bubbled through the fat at elevated temperature in the presence of a catalyst such as nickel and in the absence of oxygen.

Prior to this process, most naturally occurring unsaturated fatty acids take the cis configuration at their double bonds. Partial hydrogenation rearranges the double bonds, converting some to the trans configuration and shifting the double bonds along the carbon chain. The extent of hydrogenation determines how much the process raises a fat's melting point, turning liquid vegetable oil into products ranging from soft margarine to solid shortening.

Food companies are responding to the public's growing awareness of the downside of trans fats in a range of ways. McDonald's, for instance, announced last fall that it would replace by this February the oil in which it fries food in order to cut trans fat content in half. But CSPI says the company has since dropped these plans. McDonald's didn't respond to requests for comment.

Kraft, which has set up a Web page on trans fat as it relates to Oreo cookies, says that it is "actively exploring" ways to reduce the snack's trans fat content. Kraft states that a serving of three Oreos contains 7 g of fat, including 1.5 g of saturated fat and 2.5 g of trans fat. A serving of its reduced fat Oreos has 3.5 g of fat, including 1 g of saturated fat and 1 g of trans fat.

PepsiCo's Frito Lay division began including a trans fat line on some of its product labels earlier this year. In addition, by switching from hydrogenated oil to corn oil, the company has eliminated trans fat from Doritos, Tostitos, and Cheetos. And several of Frito Lay's other snacks are also trans fat free.