TRANS FATS, THE synthetic molecules that appear in more than 40 percent of foods on grocery shelves as “partially hydrogenated” oils or “vegetable shortening,” are a guilty pleasure for both cooks and consumers. They show up in fresh foods, making croissants flaky and pie crusts crumbly. But they’re also what’s keeping that decade-old Twinkie at the back of your pantry soft—and they’re one of the many reasons health-conscious eaters should throw that Twinkie in the trash. Trans fats have been linked to high cholesterol, clogged arteries, heart attacks, stroke and diabetes. They may be even unhealthier than the saturated animal fats they’re often intended to replace. Like “natural” saturated fats, man-made trans fats raise “bad” LDL cholesterol—and they also lower “good” HDL.