The purpose of this question is to determine your intake of the essential fatty acids called omega-3s. Omega-3s may help reduce the risk and symptoms of many disorders such as heart disease, cancer, macular degeneration (age-related blindness), arthritis, and all inflammatory disorders. These fatty acids are found primarily in oily fish that live in cold water, especially salmon, mackerel, sardines, herring, and, to a lesser extent, albacore tuna. Wild Alaskan salmon (which may have more omega-3s than farmed salmon) is my first choice because it's both tasty and relatively free of the environmental toxins that contaminate many species of fish. If fresh salmon is not feasible for you, then canned salmon is an acceptable choice.
My longstanding recommendation is to consume two to three servings of fish per week. A 3-ounce serving of Alaskan salmon or herring contains about 2 grams of omega-3 fatty acids, while 3 ounces of sardines has about 1.3 grams.
Fish is not the only source of omega-3 fatty acids. Walnuts, flaxseed, and hemp provide alpha-linolenic acid, which the body converts to the omega-3 fatty acids it needs. You can substitute one ounce of walnuts for a serving of fish, or add a tablespoon or two of freshly ground flaxseed, or hemp oil to your diet. The only problem with plant sources of these nutrients is that some people may not be able to convert alpha-linolenic acid to the longer-chain forms that occur in fish (which are the ones the body needs).
I am not opposed to taking a good quality fish oil supplement if you are not getting an adequate amount in your diet, particularly if you have any of the following health conditions: high cholesterol, diabetes, symptoms of PMS, coronary artery disease, breast cancer, memory loss, depression, insulin resistance, high cholesterol, or rheumatoid arthritis. Don't forget to try the Vitamin Advisor, it takes your health conditions into account and calculates how much of each ingredient goes into your recommended formula.
Andrew Weil, M.D.