Omega-3 fatty acids refer to a group of polyunsaturated fatty acids found in certain foods. Alpha-linolenic acid is considered an essential fatty acid (EFA) for humans because the body cannot make it from other fatty acids. It is 18 carbons long and found in plant foods, specifically flax seeds, walnuts, hemp seeds, and certain greens like purslane. Ground flax seed is the best source of this fatty acid. EPA and DHA (docosahexaenoic acid) are long chain omega-3 fatty acids, 20 and 22 carbons long, respectively. They are found in animal foods (fish and wild game) as well as in some algaes. They are the primary constituents of fish oils that seem to protect against heart attack, stroke, cancer and inflammatory diseases like rheumatoid arthritis. EPA is involved in protection against disease in several ways. The most important include "thinning" the blood and preventing blood clots, and being converted into less inflammatory prostaglandins and reducing inflammation. Oily fleshed, cold water fish like salmon and sardines are the best sources of EPA, although fish oil capsules are available and may be used if higher amounts of EPA are needed for specific conditions. If you use fish oil capsules, choose a product that is free from heavy metals and toxins that may also contaminate fish.