Solid shortening, the thick white paste that made your grandmother’s piecrust so flaky, was created nearly a century ago by adding hydrogen to liquid oils to make them turn solid at room temperature (the process known as hydrogenation). Originally intended as a cheap substitute for butter and lard, partially hydrogenated oils soon became known for their ability to increase the shelf life and improve the texture of baked goods and other food products. Soon food manufacturers were adding them to everything from cookies to nondairy creamers to frozen foods, and restaurants were using them for deep-frying and more. These days the trend is moving in the opposite direction.

More About the Fat We Love to Hate

In 1994 a study at Harvard University reported that people who consumed the highest amounts of trans fats had twice the heart-attack risk of those who consumed little. “The more we look at trans fat,” says Walter Willett, who worked on the study, “the more we see it is a metabolic poison.” Trans fats are particularly harmful because they lower levels of good cholesterol and raise levels of bad cholesterol.

Earlier this year, the U.S. Food and Drug Administration began requiring food manufacturers to list trans fats (often called partially hydrogenated oils) on nutrition labels, which prompted many food companies, including Kraft, Campbell’s, and Wendy’s, to reduce or remove trans fats from their products. Unfortunately, many companies replace trans fats with saturated fats.

To keep things in perspective, trans fats make up just 1.5 to 2.5 percent of most Americans’ diets, and saturated fats around 11 percent, notes Alice Lichtenstein, D.Sc., director of the Cardiovascular Nutrition Laboratory at the Jean Mayer Center on Aging at Tufts University, in Boston. “We should try to cut down on trans fats as well as saturated fats,” she says