By Dr. Leo Galland
Although the body readily makes most of the fat that it needs from dietary starch or sugar, humans lack the ability to make essential fatty acids (EFAs) and must get them from food or dietary supplements.
Essential fatty acids come in two distinct families, based upon their chemical structure. The two EFA families are not interchangeable and, in fact, tend to compete with one another in the body’s metabolic pathways.
The larger family, called "omega-six" EFAs, is abundant in many vegetable seed oils, including corn, sunflower and safflower. Deficiency of omega-six EFAs can cause impairment of growth and fertility, hormonal disturbances and immunologic abnormalities. But an excess of omega-six EFAs may promote the development of cancer. People living in North America and Europe often have relatively high levels of omega-six EFAs in their diets, because of the increased consumption of vegetable oil.
The smaller family, called "omega-three" EFAs, is most concentrated in fish oils and in flax seed oil. It is also found in green leafy vegetables. 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. Consumption of fish, flaxseed meal and soy beans supplied omega-three’s for our ancestors.
There has been a systematic depletion of omega-three EFAs from the typical modern diet because of changes in food choices and in techniques of food processing. Some theorists have traced the origins of numerous different diseases to a lifetime depletion of omega-three EFAs.
Fish oils, the other concentrated source of omega-three’s, have made front page news because of their potential ability to help prevent disorders as apparently unrelated to one another as cancer, heart attacks, and migraine headaches, and to help 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 hair; dandruff; fraying or brittle nails; menstrual cramps; premenstrual breast tenderness. Many people in the United States and Europe are short on omega-three EFAs and could benefit from having omega-three rich foods such as flaxseed, walnuts or salmon.
Research Abstracts on EFA’s:
Am J Clin Nutr. 1999 Sep;70(3 Suppl):560S-569S. Essential fatty acids in health and chronic disease. Simopoulos AP.Center for Genetics, Nutrition and Health, Washington, DC 20009 email@example.com
Comment in: Am J Clin Nutr. 2004 Mar;79(3):523-4.
Human beings evolved consuming a diet that contained about equal amounts of n-3 and n-6 essential fatty acids. Over the past 100-150 y there has been an enormous increase in the consumption of n-6 fatty acids due to the increased intake of vegetable oils from corn, sunflower seeds, safflower seeds, cottonseed, and soybeans. Today, in Western diets, the ratio of n-6 to n-3 fatty acids ranges from approximately 20-30:1 instead of the traditional range of 1-2:1. Studies indicate that a high intake of n-6 fatty acids shifts the physiologic state to one that is prothrombotic and proaggregatory, characterized by increases in blood viscosity, vasospasm, and vasoconstriction and decreases in bleeding time. n-3 Fatty acids, however, have antiinflammatory, antithrombotic, antiarrhythmic, hypolipidemic, and vasodilatory properties. These beneficial effects of n-3 fatty acids have been shown in the secondary prevention of coronary heart disease, hypertension, type 2 diabetes, and, in some patients with renal disease, rheumatoid arthritis, ulcerative colitis, Crohn disease, and chronic obstructive pulmonary disease. Most of the studies were carried out with fish oils [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)]. However, alpha-linolenic acid, found in green leafy vegetables, flaxseed, rapeseed, and walnuts, desaturates and elongates in the human body to EPA and DHA and by itself may have beneficial effects in health and in the control of chronic diseases.
Annu Rev Nutr. 2004;24:597-615. Dietary n-6 and n-3 fatty acid balance and cardiovascular health. Wijendran V, Hayes KC. Foster Biomedical Research Lab, Brandeis University, Waltham, Massachusetts 02254, USA. firstname.lastname@example.org
Epidemiological and clinical studies have established that the n-6 fatty acid, linoleic acid (LA), and the n-3 fatty acids, linolenic acid (LNA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) collectively protect against coronary heart disease (CHD). LA is the major dietary fatty acid regulating low-density lipoprotein (LDL)-C metabolism by downregulating LDL-C production and enhancing its clearance. Further, the available mass of LA is a critical factor determining the hyperlipemic effects of other dietary fat components, such as saturated and trans fatty acids, as well as cholesterol. By contrast, n-3 fatty acids, especially EPA and DHA, are potent antiarryhthmic agents. EPA and DHA also improve vascular endothelial function and help lower blood pressure, platelet sensitivity, and the serum triglyceride level. The distinct functions of these two families make the balance between dietary n-6 and n-3 fatty acids an important consideration influencing cardiovascular health. Based on published literature describing practical dietary intakes, we suggest that consumption of ~6% en LA, 0.75% en LNA, and 0.25% en EPA + DHA represents adequate and achievable intakes for most healthy adults. This corresponds to an n-6/n-3 ratio of ~6:1. However, the absolute mass of essential fatty acids consumed, rather than their n-6/n-3 ratio, should be the first consideration when contemplating lifelong dietary habits affecting cardiovascular benefit from their intake.