Trans fats became popularized when Walter Willett, M.D., chairman of the Harvard School of Public Health's Department of Nutrition, completed a study involving 80,000 women. His results showed that for every 5% increase in the amount of saturated fats a woman consumed, her risk of heart disease increased by 17%, while only a 2% increase in trans fats increased her heart disease risk by 93%. Additionally, Willett found that the risk of type 2 diabetes rose by 39% from only a 2% increase in calories from trans fats, whereas saturated fat did not affect diabetes at all.

While meat and dairy products contain small amounts of naturally-occurring trans fat, the majority of trans fat is created artificially by bubbling hydrogen gas through vegetable oil, a process called partial hydrogenation. This transforms some of the oil's unsaturated fat (the "good" fat) into trans fat, which raises LDL (the "bad" cholesterol), just as saturated fat does. Worse yet, some studies have found that trans fat lowers HDL (the "good" cholesterol), too.

So why do many food manufacturers use hydrogenated vegetable oil with full knowledge of the serious health risks of trans fats? Easy — they're great for the food industry — they keep foods from going stale so they can last longer on the shelves; they're less expensive than butter; and they're more stable, which is especially helpful for deep-frying foods.

But is trans fat really a necessary ingredient? "It is put into the food supply by the food industry and can be completely eliminated (the Europeans have almost done this) without individuals needing to make any changes in their diets," said Dr. Willett.

However, most experts feel that an all-out ban is impractical. Instead, to combat this information gap, the Food and Drug Administration (FDA) is finalizing a plan that would require trans fat labeling on packaged foods, prompted by the Institute of Medicine, a government advisory agency that has conducted a number of studies on the health risks of trans fats.

Public awareness of trans fats is already making a difference. Frito-Lay told Consumer Reports that it plans to eliminate trans fat from Cheetos, Doritos, and Tostitos, and McDonald's recently decided to cut out nearly half the trans fats from their French fries. Keep in mind, this reduction doesn't suddenly make fast food a health food — taking out the trans fat doesn't affect the calories — a super-size order of McDonald's fries still has 610 calories.

In fact, many nutrition experts think the attention given to trans fats is "overkill" in that it narrowly focuses on only one area of a person's diet. "I don't think the issue is trans fat at all. The issue is healthy eating habits. How many Krispy Kremes [doughnuts] do you need to eat? What does this add to your diet?" asks Dr. Margo A. Denke, M.D., professor of nutrition at the University of Texas Southwestern Medical Center at Dallas.

Dr. Willett agrees that overall diet is paramount, but he cautions that trans fats still pose a formidable health risk: "The risks of obesity are worse than eating large amounts of any kind of fat. However, we see that the combination of obesity and high trans fat intake is a particularly bad one for risk of type 2 diabetes."

So what is an acceptable level of trans fat?

"Because they are not essential and provide no known health benefit to human beings, there is no safe level of trans fatty acids, and people should eat as little of them as possible while consuming a nutritionally adequate diet," said Barbara Schneeman, professor of nutrition at the University of California, Davis. "But I'm much more concerned about excess calories that are consumed — because almost as a matter of course items that contain trans fatty acids are high in calories [fried foods and bakery items]," added Dr. Schneeman.

The bottom line is a familiar one: consume as little trans fat and saturated fat as possible, and maintain a healthy weight. Most researchers recommend reducing your intake of saturated and trans fats to less than 10% of calories, or 20 grams per day of both fats combined.

Because the trans fat content is not yet available on most food labels, Consumer Reports and other health experts offer the following recommendations for identifying trans fatty acids:

• Know "suspect" foods: Look out for trans fats in many margarines and shortenings, deep fried foods, fast foods, and many commercial baked goods such as pies, cookies, cakes, crackers and doughnuts, and other common packaged items. Exceptions include potato chips, pretzels, peanut butter and salad dressings.
• It might sound healthy: Some packaged foods that sound "healthy" have trans fat lurking, including Mrs. Smith's Apple Pie, Nabisco Wheat Thins, Kellogg's Cracklin' Oat Bran Cereal, Kellogg's Eggo Buttermilk Frozen Waffles, and Pillsbury Buttermilk Frozen Waffles.
• Check the ingredients: Look for shortening or partially hydrogenated oil in the ingredients list; the closer they are to the beginning of the list, and the more total fat on the label, the more trans fat the product probably contains.
• Do the math: If a product lists saturated, monounsaturated, and polyunsaturated fats, check to see if those numbers add up to the total fat listed. If they don't, there's a good chance trans fat makes up for some of the difference.
• Watch what they "claim": Products can claim to be "low saturated fat" or "extra lean" even if they contain trans fats.
• It may not matter: The combined total of trans and saturated fat matters most. There is little benefit in choosing a food that's low in trans fat if it's high in saturated fat, and vice versa. For example, Consumer Reports revealed that Banquet Chicken Pot Pie had just a trace of trans fat, but contains 7.5 grams of saturated fat.
• Go soft: Look for soft or liquid margarines instead of hard margarines; the softer the margarine, the less trans fat it contains. And don't go running to butter just yet — butter also contains trans fats, not to mention loads of saturated fats.