"Artificial trans fats are vegetable oils that have had hydrogen atoms added so they turn from liquid into solid," says Katherine Tallmadge, RD, spokesperson for the American Dietetic Association. "Food manufacturers like to use them because they're cheap, give products a longer shelf life and enhance the flavor and texture of foods-for instance, they make cookies crispier and pie crusts flakier. Years after they were invented, we discovered that trans fats deliver a double whammy to our health. They both raise LDL (artery-clogging bad cholesterol that leads to heart attacks) and, in large amounts, decrease HDL (fat-clearing good cholesterol)." The American Heart Association also links trans fats to an increased risk of type 2 diabetes.

Why Are They Used?
Although trans fats are found in small amounts naturally (primarily in some animal-based foods), almost all of what we get in our daily diets are manufactured. They're created when food makers add hydrogen to vegetable oil, a process called hydrogenation, which turns liquid oils into stable, long-lasting solids, such as shortening and many stick margarines. If you see "partially hydrogenated vegetable oil" on an ingredient list, you know the food contains trans fats. The food industry loves these fats: They're a cheap, effective way to make crackers crunchy, french fries crispy, cookie fillings creamy and frozen foods more flavorful. They also extend these products' shelf lives.