Q: What is a trans fat?

A: These fats — also known as trans fatty acids — are made by adding hydrogen to liquid oil, which turns it into a solid, like stick margarine. This makes it a handy ingredient for processed-food manufacturers, since it improves the texture, stability and shelf life. It’s also inexpensive. It’s often used in foods including microwave popcorn, coffee creamers, packaged cookies, cans of frosting and frozen pizza, among others.

Q: Where does it come from?

A: Trans fats are a natural component of animal products such as milk and meat. The FDA says that it is synthesized in the guts of grazing animals.

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Artificial trans fats were invented in 1901 by Wilhelm Normann. The German chemist added hydrogen gas to liquid oils and came up with a cheaper alternative to natural products such as lard and butter. For many years, these partially hydrogenated oils were believed to be safer than trans fats from animals, according to the Center for Science in the Public Interest, or CSPI. But by the early 1990s, epidemiologists were realizing that the fats contributed to heart disease.

Q: Why are trans fats bad for your health?

A: It’s not just bad, it’s doubly bad. For one thing, it increases blood levels of the “bad” cholesterol, low-density lipoprotein. High levels of LDL increase one’s risk of coronary heart disease, including angina, heart attacks and other potentially fatal problems, according to the Centers for Disease Control and Prevention (CDC).

To make matters worse, researchers also think that trans fats reduce blood levels of high-density lipoprotein, the “good” cholesterol, or HDL. HDL appears to reduce heart risks by funneling blood cholesterol to the liver, where it’s broken down and removed from the body. There’s also evidence that HDL slows the buildup of dangerous plaques in the arteries, the American Heart Association says.

Q: What exactly happened Thursday?

A: The FDA announced its intent to remove partially hydrogenated oils from its list of ingredients that are “generally recognized as safe” (GRAS). That would effectively prevent food makers from using it in products.

Members of the public will have 60 days to comment on the proposal. If the ban takes effect, it would mark the first time since 1969 that an item has been removed from the GRAS list. Then, the artificial sweetener cyclamate was knocked off the list due to concerns about bladder cancer, liver damage and birth defects. Subsequent studies have found it to be safe in humans.

Q: What are partially hydrogenated oils?

A: These are the primary source of artificial trans fats.