essential fatty acid (EFA), a polyunsaturated acid, such as linoleic, alpha-linolenic, and arachidonic acids, essential in the diet for proper growth, maintenance, and functioning of the body. EFAs are prostaglandin precursors that play important roles in metabolism. They are also necessary for the normal functioning of the reproductive and endocrine systems and the breaking up of cholesterol deposits on arterial walls. The best dietary sources are natural vegetable oils, such as soy and corn oils; margarines blended with vegetable oils; wheat germ; edible seeds, such as pumpkin, sesame, and sunflower; and fish oils, especially cod liver and other fish body oil. Although rare, a deficiency of EFAs causes changes in cell structure and enzyme function, resulting in decreased growth and other disorders. Symptoms include brittle and lusterless hair, nail problems, dandruff, allergic conditions, and dermatoses, especially eczema in infants. Also excessive amounts may reduce the level of vitamin E in tissues and cause other metabolic disturbances.
