The three primary omega 3s are alpha-linolenic acid (ALA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). In the marine-based omega 3s (DHA and EPA), algae is the first source of omega 3, which moves up the marine food chain through bioaccumulation, giving large, fatty, cold water, marine fish the highest concentrations. ALA omega-3 is the land based omega 3 and can be found in nuts, seeds and many vegetables, with notably high concentrations in chia, flax, walnuts and avocados. Unfortunately, while ALA could be potentially an adequate omega 3 source if on an extremely low omega 6 content diet, it may not be a viable source for most of us. In the human body, ALA must be converted to EPA and then to DHA in order to produce the bioactive products but the conversion can be anywhere between 0.2-20%.
