A: Trans fats, also called partially hydrogenated oils, are created when hydrogen is added to vegetable oil to make it more solid. They can contribute to heart disease and are considered even less healthy than saturated fats, which also cause heart problems.
Q: How do I know if I am eating them?
A: You won't be able to taste them, but they do help give a more solid texture to certain foods, like baked goods and ready-to-eat frostings. Some restaurants use them to fry food and they are also used in microwave popcorn, biscuits and pie crusts. You'll know you are eating them by looking on the nutrition label of a packaged food — the FDA has required labeling of trans fats since 2006.
Q: Why are they so bad for you?
A: Trans fats can raise "bad" cholesterol and lower "good" cholesterol. That can contribute to heart disease — the leading cause of death in the United States.
Q: Are all fats bad for you?
A: No, but they should be eaten in moderation. Saturated fats found in nuts, vegetable oils and fish are the best for you. Saturated fats mostly derived from animals are less healthy and should be less than 10 percent of a person's daily calories. Total fat should make up no more than 35 percent of calories a day, according to the federal Centers for Disease Control and Prevention.
Q: How will the trans fats be phased out?
A: The FDA announced Thursday that it has made a preliminary decision that trans fats no longer fall in the agency's "generally recognized as safe" category, which is reserved for thousands of additives that manufacturers can add to foods without FDA review. Once trans fats are off the list, anyone who wants to use them would have to petition the agency for a regulation allowing it. Such a petition would be unlikely to be approved since the FDA has determined that trans fats are a threat to public health. The agency hasn't yet said what the timeline will be for eliminating them.
Q: Haven't a lot of trans fats already been phased out?
A: Yes. A series of local laws, starting with New York City in 2008, has already prompted the food industry to find alternatives. The industry estimates that almost three-fourths of trans fats are gone already. According to the FDA, trans fat intake among Americans declined from 4.6 grams per day in 2003 to around one gram in 2012.
Q: If many are gone already, then what are the benefits of phasing them out?
A: The FDA is aiming to get rid of those trans fats that are left in the marketplace. Commissioner Margaret Hamburg said the move could prevent 20,000 heart attacks and 7,000 deaths a year.
Q: Will it be hard to find substitutes?
A: In some cases, no. Frying oils are easily substituted and food scientists have already figured out how to substitute other fats for trans fats. In other cases, it will be harder. Ready-to-eat cake frosting, for example, gets some of its solid shape from trans fats. Companies will have to figure out how to keep the item the same without them.
Q: Will I notice the change?
A: Probably not. Trans fats don't have any particular taste, and in most cases other fats will simply be substituted. Your heart might notice, though. Michael Jacobson of the Center for Science in the Public Interest says the prohibition is "one of the most important lifesaving actions the FDA could take."