When it comes to fat, trans fat is considered by some doctors to be the worst of them all because of its double-barreled impact on your cholesterol levels. Unlike other fats, trans fat (also called trans fatty acids) raises your "bad" (LDL) cholesterol and lowers your "good" (HDL) cholesterol.

Trans fat comes from adding hydrogen to vegetable oil through a process called hydrogenation. Trans fats are more solid than oil, making them less likely to spoil. Using trans fats in the manufacturing of foods helps foods stay fresh longer, have a longer shelf life and have a less greasy feel.

Commercial baked goods, such as crackers, cookies and cakes, and many fried foods, such as doughnuts and french fries, contain trans fats. Shortenings and some margarines also are high in trans fat.