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alexandra_k said:
i got flax seed oil (omega 3, 6, 9).
part of the reason was that i wasn't sure whether the fish oil was okay with respect to heavy metal accumulation in the fish...

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Flax oil is fine as a source of alpha-linolenic acid, but nobody needs extra omega-6 fatty acids, with the modern diet full of vegetable oils.

There is no heavy metal associated with fish oils. Metals are mopped up by proteins and all protein is removed from fish oils before they get to market. There are no detectable heavy metals in fish oil.

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another part of the reason is that i'm not at all sure that the fish oil is harvested in a sustainable fashion and i'm concerned about nets capturing dolphins (for example) and just generally speaking i think we are better not to harm living things (who might feel pain given that they have a nervous system) over flax, for example (that lacks a nervous system).

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By and large, all commercial fish oil is made from the byproducts of fish destined for the table. In some regions, fish oil is burned for power, there is such a glut from the fish processing industry. Better consumed as a nutrient, than burned.

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[same active ingredients...

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That is incorrect. Flax oil (and all other vegetable oil sources of omega-3) contain the 18-carbon, thrice unsaturated fatty acid known as alpha-linolenic acid. It was long believed that this fatty acid was essential, and served as a precursor for the (truly) essential fatty acids EPA (20-carbon, five times unsaturated), and DHA (22-carbons, six times unsaturated). Recent experiments using radio-labelled alpha-linolenic acid have shown that only about 5% makes it to EPA, and less than 0.1% (an average, nil in most subjects) made it so far as DHA. The elongase and desaturase enzymes we thought could do the trick are woefully ineffecient. DHA is now being declared fully essential, i.e. it must be obtained from diet.

DHA is found in some marine algae, and there are a couple of algal-based oil products on the market, for the vegans out there. Otherwise, seafood is the only alternative.

Lar