The larger family, called "omega-six" EFAs, are abundant in many vegetable seed oils, including corn, sunflower and safflower. Deficiency of omega-six EFAs causes impairment of growth and fertility, hormonal disturbances and immunologic abnormalities. An excess of omega-six EFAs may promote the development of cancer. People living in North America and Europe have relatively high levels of omega-six EFAs in their diets, because of the increasing consumption of vegetable oil during the twentieth century.

The smaller family, called "omega-three" EFAs, is most concentrated in fish oils and in flax seed (linseed) oil. It is also found in green leafy vegetables and in the flesh of animals that feed on grass and leaves. The human brain is rich in omega-three EFAs; their deficiency causes abnormalities in the development and function of the nervous system as well as immune defects. Omega-three EFAs formed an important part of the diet of Stone Age humans, who relied heavily on wild game and leafy plants for nourishment. Consumption of fish, flax seed meal and soy beans supplied omega-three's for our more recent ancestors. The past century has witnessed a systematic depletion of omega-three EFAs from the Western diet because of changes in food choice and in techniques of animal husbandry and food processing. Some theorists have traced the origins of numerous different diseases to a lifetime depletion of omega-three EFAs.

Extensive research published since 1985 has demonstrated that flax oil can prevent cancer and birth defects in animals. Fish oils, the other concentrated source of omega-three's, have made front page news because of their ability to prevent disorders as apparently unrelated to one another as cancer, heart attacks, migraine headaches, and premature births, and to reverse the effects of conditions as different as psoriasis, ulcerative colitis, rheumatoid arthritis and cystic fibrosis.

Some indications that an EFA deficiency or imbalance are present are: dry skin; the need to use moisturizing creams and lotions; "chicken skin", the presence of tiny rough bumps, usually on the back of the arms; dry or unruly hair; dandruff; soft, fraying or brittle nails; menstrual cramps; premenstrual breast tenderness. A person who has these symptoms will often find that they improve by supplementing an otherwise healthy diet with the appropriate oil. Discovering the appropriate oil requires a bit of personal experimentation. Most people in the United States and Europe are short on omega-three EFAs and will benefit from supplementing their meals with flax oil (one tablespoon a day). Flax oil should be stored in the dark and in the refrigerator; it should not be used for cooking.

Virtues of the GLA
Although most Americans consume more than enough of the omega-six EFAs, there is a small but significant proportion of the population (about fifteen per cent, if my patients are in any way representative), who are unable to properly metabolize omega-six EFAs and will benefit from supplementation with oils that are rich in omega-six's. The three most useful omega-six rich oils are evening primrose oil, borage oil and black currant seed oil, all of which are sold in capsule form. These oils contain a special EFA called gamma-linolenic acid (GLA), which allows the body to overcome the most common impediment to proper utilization of omega-six EFAs. Although experimental data indicate that feeding large doses of omega-six rich oils, such as corn oil or safflower oil, can promote the growth of cancer, there is no evidence that feeding GLA in the form of primrose oil contributes to cancer. Quite the contrary, primrose oil behaves like the omega-three rich oils (flaxseed and fish) in actually preventing tumor growth in experimental animals. The usual requirement for GLA among those who need it is supplied by taking four to six capsules of evening primrose oil, two to three capsules of borage oil, or three to four capsules of black currant seed oil every day (assuming each capsule contains five hundred milligrams of oil). I generally reserve GLA supplements for people whose dryness does not respond to omega-three supplementation. Because the omega-three and omega-six EFAs compete with one another in the body, feeding fish oil to a person who needs GLA may actually increase that person's omega-six deficit, making the skin dryer or the breasts more tender. An increase in these symptoms with omega-three supplements is almost surely a sign to switch to GLA. Lack of response is usually a reason to add GLA. Controlled studies have demonstrated therapenefits for GLA in people suffering from arthritis, eczema and premenstrual syndrome. What is important in making therapeutic decisions, however, is not the disease but the patient. EFA therapy does not treat disease, it improves cellular function.