The essential fatty acids (EFA) include linoleic, linolenic, and arachidonic acids, collectively termed vitamin F. They are all polyunsaturated fatty acids that cannot ordinarily be synthesized in the body; although, if sufficient quantities of linoleic acid (omega-6) are present, arachidonic acid can be made. Alpha-linolenic, an omega-3 fatty acid that is found in special oils such as linseed (flax), rapeseed (canola), and soybean, is also essential and is the precursor of other important omega-3 oils EPA and DHA commonly found in fish. Ideally we need more linolenic, about a 2:1 ratio, than linoleic. The essential fatty acids are important for normal growth, especially of the blood vessels and nerves, and to keep the skin and other tissues youthful and supple through their lubricating quality.

Linoleic acid is necessary for synthesis of prostaglandins in the E1 and E2 series; linolenic acid is the precursor of the E3 series and other omega-3 fatty acids. Prostaglandins, hormonelike substances, have various effects on smooth muscle and inflammatory processes. The E3 (PGE3) series seems to reduce cholesterol levels as well as platelet aggregation and thrombosis and are generally anti-inflammatory. Prostaglandin E2, related to arachidonic acid, tends to promote platelet aggregation, is more inflammatory, and may even be related to high blood pressure and cancer. PGE1 is mildly inflammatory as it prevents release of arachidonic acid from the cells. Safflower oil is particularly high in linoleic acid, as are sunflower and corn oils; other vegetable oils, nuts, and seeds are also good sources. As stated, soybean, flaxseed, canola, as well as pumpkin and walnut are the best sources of alpha-linolenic acid. (See Vitamin F, Chapter 5, Vitamins.)

Another fatty acid recently shown to be beneficial is eicosapentaenoic acid (EPA). It is a polyunsaturated, omega-3 fatty acid found in high concentrations in cold-water fish. Where it is consumed in large amounts, as among Greenland Eskimos or in fishing villages in Japan, there is reduced cardiovascular disease. EPA seems to reduce serum triglycerides, raise HDL (good) cholesterol, and prolong bleeding time by reducing platelet aggregation, thus preventing thrombosis. Fish such as mackerel, sardines, and salmon are high in eicosapentaenoic acid. Consumption of cold-water fish once or twice a week seems to have a positive effect on cholesterol levels. When taken as a supplement such as MaxEPA (there are many products now available), which contains EPA and another omega-3 fatty acid, decosahexaenoic acid (DHA), may decrease the risk of vascular thrombosis and cardiovascular disease. (See more on EPA in Chapter 7, Accessory Nutrients.)

Phospholipids
Phospholipids, of which the most common is lecithin, are important in the structure of all membranes. Their structure is similar to that of triglycerides, but they contain only two fatty acids (both polyunsaturated). The third molecule attached to the glycerol is a phosphatidylcholine molecule (choline is one of the B vitamins). Certain phospholipids also contain inositol (another B vitamin) as phosphatidylinositol, as well as phosphatidylethanolamine, another phospholipid that has several functions, such as being a precursor to choline and acetylcholine. Lecithin is found in highest concentration in soybeans and egg yolks. Recently, egg lecithin has been used in the treatment of acquired immune deficiency syndrome (AIDS). There is some question as to whether supplemental lecithin helps to lower cholesterol levels. It seems to have a mild influence, perhaps due to its polyunsaturated nature. Because of their carbohydrate-fat construction, phospholipids move well in fats as well as in water and thus move easily