Hydrogenation, complete or partial, is a chemical process in which hydrogen is added to liquid oils to turn them into a solid form. Partially hydrogenated fat molecules have trans fats, and they may be the worst type of fat you can consume. Don’t confuse these man-made trans fats with those that occur naturally in some foods. Only chemically altered trans fats have been shown to increase cholesterol levels, which can lead to a host of cardiovascular problems.
Q. What is trans fat?
A. Most trans fat is a monounsaturated (one double bond) fatty acid. The shape of trans-fat molecules is more like cholesterol-raising saturated fat than a typical monounsaturated fatty acid. Perhaps for that reason, it increases cholesterol levels in blood and increases the risk of heart disease.
Q. Where does trans fat come from?
A. According to the Food and Drug Administration (FDA), in 1994-96 we consumed about 5.6 grams of trans fat per day. Most of that trans fat comes from the 40,000-plus foods that contain partially hydrogenated vegetable oil. Those include many stick margarines, biscuits, pastries, cookies, crackers, icing, and deep-fried foods at restaurants. Because Frito-Lay, margarine producers, and some other companies recently stopped using (or cut back on the use of) partially hydrogenated oils, we now are consuming a little less trans fat. About one-fifth (1.2 g) of the trans fat came from natural sources, especially beef and milk products (bacteria in cattle produce trans fat that gets into meat and milk) . A little more occurs naturally in vegetable oils and forms when vegetable oils are purified.
Q. How is partially hydrogenated oil made?
A. To convert soybean, cottonseed, or other liquid oil into a solid shortening, the oil is heated in the presence of hydrogen and a catalyst. That hydrogenation process converts some polyunsaturated fatty acids to monounsaturated and saturated fatty acids. It also converts some monounsaturated fatty acids to saturated fatty acids. Thus, a healthful oil is converted into a harmful one. The problem arises when some of the fatty acids are converted to the “trans” form. The term “trans” comes from the fact that two parts of fatty acid molecules are on opposite sides of double bonds. In the usual “cis” fatty acids, the two parts are on the same side of the double bonds. The degree of hydrogenation determines how solid the final product will be and how much of the different fatty acids it will contain.
Q. Why are oils partially hydrogenated?
A. To increase shelf life and obtain the cooking properties of solid shortenings, oils are partially hydrogenated. That eliminates most of the unstable fatty acids—those with three or two double bonds. Partially hydrogenated oils have been used to replace butter, lard, palm oil, coconut oil, and other “hard” fats in such foods as many processed foods. Fortunately, food technologists have been figuring out increasingly better ways to make those foods taste better without hard fats.
Q. Are fully hydrogenated oils even worse than partially hydrogenated oils?
A. No. Surprisingly, fully hydrogenated oils appear to be innocuous. In the case of fully hydrogenated soybean oil, the hydrogenation process increases the amount of saturated fat, but most of that fat is stearic acid. Stearic acid does not raise “bad ” (LDL) cholesterol levels, because the body converts it quickly to monounsaturated oleic acid (the characteristic fatty acid in olive oil).
Q. Why are partially hydrogenated oil and trans fat so bad for your health?
A. Trans fat increases the amount of “bad” (LDL ) cholesterol in blood, and that increases the risk of heart disease. It also decreases the “good” ( HDL) cholesterol, which may increase the risk of heart disease even more. Preliminary research suggests that trans fat might have additional harmful effects on the body . Finally, the hydrogenation process destroys some of the vitamin K in vegetable oil, which might be a problem for consumers who have marginal intakes of that vitamin.
Q. How bad is trans fat?
A. Extrapolating from estimates made by the FDA ,replacing with more healthful ingredients all the trans fat that comes partially hydrogenated oils likely would save upwards of 10,000 lives a year.
Q. So should I avoid every molecule of trans fat?
A. Not necessarily. Trans fat is not a toxin that will kill everyone who eats even a tiny amount. It’s worth avoiding foods in which partially hydrogenated oil is one of the first few ingredients on the label, but not worth worrying about if partially hydrogenated oil is down near the end of the ingredient list. (Ingredients are listed in order of predominance.)
Q. With what ingredients would companies replace partially hydrogenated oil?
A. In the case of margarine, many fried foods, and some baked foods, companies often use canola oil, sunflower oil, and other liquid oils. When a solid fat cannot be avoided, companies might use palm oil, butter (though rarely, because it is expensive), beef tallow, or lard. Ideally, companies would work hard to use less of those saturated fats, perhaps mixing them with a liquid oil.
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