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"However, for heart health, a fish oil dietary supplement is recommended by most medical experts and naturopathic practitioners. ALA needs to be converted to DHA and EPA in the body....and this conversion does not always take place, especially for people who are in less than optimal health. This would include many elderly folks. On the other hand, if you're in good health flax seed ALA may be converted by the body to DHA and EPA.

Thus, when the heart is concerned in the flax oil vs fish oil debate, fish oil wins in our opinion since you can get the crucial DHA and EPA directly through a quality fish oil. For brain health and symptoms like depression, a fish oil dietary supplement is recommended for much the same reasons.

The brain needs large amounts of DHA, but if the body needs the ALA for some other reason, it may not ever be converted to DHA."
from this article

We evolved eating meat and fish.