Avoiding saturated fat and cholesterol is already mainstream practice for health-minded shoppers. But there’s a new villain in town: trans fats. Ubiquitous in processed foods, trans fats increase heart-disease risk and may contribute to diabetes, stroke, and cancer.

“People are just starting to get that trans fats are bad, but they don’t know why,” says Kim Severson, food reporter and author of The Trans Fat Solution (Ten Speed Press, 2003). Food labels increasingly cluttered by health claims often confound the problem. Here, we break down what trans fats are and offer tips on how to avoid them in your diet.

How trans fats form
Trans fatty acids are created when hydrogen is added to a liquid fat, forcibly changing its melting properties so it remains solid at room temperature—a desirable quality for products such as margarine and shortening. The prefix “trans” refers to carbon bonds that, during hydrogenation, are folded against their natural direction, forming a fat that’s artificially saturated. Hydrogenation improves shelf life, flavor stability, and “mouthfeel,” but it’s the birthplace of trans fats.

Like saturated fat and dietary cholesterol, trans fats raise LDL (bad) cholesterol, which accumulates on artery walls. Even worse, trans fats may lower HDL (good) cholesterol, which transports cholesterol back to the liver for disposal. In fact, compared with saturated fats, trans fats consumption correlates to a considerably higher risk for heart problems caused by narrowed arteries (Annals of Nutrition and Metabolism, 2004, vol. 48, no. 2).

Although trans fats exist in small amounts in animal products, of greater concern are those hiding in processed foods. They’re abundant in cookies, crackers, chips, cakes, and margarine, foods that contribute 75 percent of the trans fats in a typical U.S. diet.

How to avoid trans fats
Look before you buy. “Always look for the words ‘partially hydrogenated’ on the ingredient list” of any food, says Severson. “That tells you the product has trans fats. How much depends on how high up on the list the words are and how big a serving you have.” If partially hydrogenated appears at or near the top of the list, pick an alternative that uses nonhydrogenated oils, such as canola or olive.

Watch what you eat. Fried foods are trans fat troves; a typical doughnut harbors 3.2 trans fat grams, and a large order of fries serves up a whopping 6.8 grams. And keep in mind that restaurants may be frying up more than spuds; ask how chicken, breaded zucchini, fish, breakfast foods, and tortillas are prepared before ordering them. Because of increased awareness (and thanks to customers who speak up), many eateries are now frying with 100 percent corn oil, a trans fat-free, polyunsaturated oil.

Use all fats sparingly. By moderating total fat intake, you’ll automatically reduce trans fats. The American Heart Association recommends a daily total fat intake of 5 to 8 teaspoons (25 to 40 grams), with the focus on good-fat sources such as nuts, fish, olive and canola oils, avocados, and flax or hemp seed, and no more than 10 percent of total calories from saturated and trans fats.

Adjust your cooking routine. In many recipes, total fat can be reduced by at least one-fourth with no discernible effect. Instead of relying on margarine or shortening, experiment with nut butters and mono- or polyunsaturated-rich oils when cooking, baking, even buttering your bread. Tipping the balance toward healthier fats will improve your cholesterol profile and even reduce breast cancer risk (Archives of Internal Medicine, 1998, vol. 158, no. 1).

Go natural. By consistently selecting less processed foods—a baked potato instead of french fries, a handful of almonds instead of chips—you’ll make a big difference in your fat-profile intake.

gThe future of fats
As scientific evidence mounts against trans fats and as consumer awareness increases, food manufacturers are voluntarily replacing trans fats with vegetable oils. New “no trans” labels are appearing on some typically trans-fat-heavy foods, especially chips and crackers—and they’re flying off store shelves, according to Stephanie Childs, spokeswoman for Grocery Manufacturers of America. But take note: The FDA allows foods containing up to 0.5 grams of trans fats to carry a trans-fat-free label, so keep track of portion sizes.

Last year, Denmark became the world’s first country to ban foods containing oils and fats with more than 2 percent industrially produced trans fats. In 2006, a new FDA rule will require trans fat information to be added to all U.S. nutrition labels. Until then, read labels diligently, and stock your pantry and fridge with good-fat sources.

Sharon Palmer is a registered dietitian who makes her home in the chaparral hills of Southern California with her husband and two sons.