Fats, or lipids, are a group of chemical substances in food that are generally insoluble in water. There are several classes of fats. The triglycerides (triacylglycerols) are the predominant constituent of vegetable and animal fats and oils. They are composed of a 3-carbon glycerol backbone and three fatty acids of various types. The character of the fat is determined by these fatty acids. Saturated fatty acids tend to make the fat "hard" or solid at room temperature and are associated with an increased risk of heart disease. Monounsaturated fatty acids are prominent in olive and canola oils and do not increase the risk of heart disease. The third group of fatty acids, the polyunsaturated fatty acids, are important components of omega-3 fish and plant oils. They play a role in blood clotting and in inflammatory responses in the body.
Phospholipids are closely related to triacylglycerols, except that one of the carbons on the glycerol contains one of several phosphate groups; the other two carbons have fatty acids. A third group, related to the first two, is the sphingomyelins and other complex brain lipids.
Cholesterol and its precursors are another group of fats that are essential for membranes; these are chemically composed of several 5-and 6-membered carbon rings. Steroids make up a fifth group of fats. Steroids are derived from cholesterol and include the androgens and estrogens, among others.
GEORGE A. BRAY