If you've ever eaten a packaged cookie or cracker or spread hard margarine on your bread, you've likely gulped down partially hydrogenated oils (called trans fats) without realizing it. But these oils, which extend the shelf life of foods, will soon disappear from products in the United States. The FDA ruled in June that it will no longer recognize partially hydrogenated oils as safe for use in food and will require companies that want to use them to seek FDA approval—not expected to be an easy task. Why the fuss? Many studies, stimulated by research here at Harvard, have shown that trans fats increase "bad" LDL cholesterol, decrease "good" HDL cholesterol, raise the risk of blood clots, and boost inflammation—all of which increase the risk of heart disease, stroke, and diabetes. It's even estimated that removing artificial trans fats from the U.S. food supply would prevent as many as 200,000 heart attacks a year. But the oils won't disappear overnight. The FDA is giving companies until 2018 to stop using partially hydrogenated oils in foods or file for an FDA okay. Until then, keep reading ingredient lists, and avoid foods with partially hydrogenated oils and trans fats.