This is a good article from Dr Andrew Weil on the differences between Omega 3 and Omega 6 fatty acids.
Omega-3 and omega-6 are types of essential fatty acids – meaning we cannot make them on our own and have to obtain them from our diet. Both are polyunsaturated fatty acids that differ from each other in their chemical structure. In modern diets, there are few sources of omega-3 fatty acids, mainly the fat of cold water fish such as salmon, sardines, herring, mackerel, black cod, and bluefish. There are two critical omega-3 fatty acids, (eicosapentaenoic acid, called EPA and docosahexaenoic or DHA), that the body needs. Vegetarian sources, such as walnuts and flaxseeds contain a precursor omega-3 (alpha-linolenic acid called ALA) that the body must convert to EPA and DHA. EPA and DHA are the building blocks for hormones that control immune function, blood clotting, and cell growth as well as components of cell membranes.
By contrast, sources of omega-6 fatty acids are numerous in modern diets. They are found in seeds and nuts, and the oils extracted from them. Refined vegetable oils, such as soy oil, are used in most of the snack foods, cookies, crackers, and sweets in the American diet as well as in fast food. Soybean oil alone is now so ubiquitous in fast foods and processed foods that an astounding 20 percent of the calories in the American diet are estimated to come from this single source.
The body also constructs hormones from omega 6 fatty acids. In general, hormones derived from the two classes of essential fatty acids have opposite effects. Those from omega-6 fatty acids tend to increase inflammation (an important component of the immune response), blood clotting, and cell proliferation, while those from omega-3 fatty acids decrease those functions. Both families of hormones must be in balance to maintain optimum health.
Many nutrition experts believe that before we relied so heavily on processed foods, humans consumed omega-3 and omega-6 fatty acids in roughly equal amounts. But to our great detriment, most North Americans and Europeans now get far too much of the omega-6s and not enough of the omega-3s. This dietary imbalance may explain the rise of such diseases as asthma, coronary heart disease, many forms of cancer, autoimmunity and neurodegenerative diseases, all of which are believed to stem from inflammation in the body. The imbalance between omega-3 and omega-6 fatty acids may also contribute to obesity, depression, dyslexia, hyperactivity and even a tendency toward violence. Bringing the fats into proper proportion may actually relieve those conditions, according to Joseph Hibbeln, M.D., a psychiatrist at the National Institutes of Health, and perhaps the world’s leading authority on the relationship between fat consumption and mental health. At the 2006 Nutrition and Health Conference sponsored by the University of Arizona’s College of Medicine and Columbia University’s College of Physicians and Surgeons, Dr. Hibbeln cited a study showing that violence in a British prison dropped by 37 percent after omega-3 oils and vitamins were added to the prisoners’ diets.
If you follow my anti-inflammatory diet, you should get a healthy ratio of these fatty acids. In general, however, you can cut down on omega-6 levels by reducing consumption of processed and fast foods and polyunsaturated vegetable oils (corn, sunflower, safflower, soy, and cottonseed, for example). At home, use extra virgin olive oil for cooking and in salad dressings. Eat more oily fish or take fish oil supplements, walnuts, flax seeds, and omega-3 fortified eggs. Your body and mind will thank you.
Andrew Weil, M.D.