Omega-3 and Omega-6 (n-6) fatty acids constitute the two families of Essential Fatty Acids (EFAs).
EFAs are considered "essential" because they are needed throughout the human life cycle, cannot be produced in the human body, and therefore must be provided through the diet.
EFAs aid in the maintenance of cell membrane fluidity and stability, development and function of brain and nerve tissue, oxygen transfer and energy production, immune functions, and conversion into compounds involved in all body functions including local hormones governing inflammatory responses.
Omega-3 fatty acids from fish is a direct source of EPA and DHA, while flax seed oil yields ALA which then must be converted into EPA and DHA. The human conversion of ALA to EPA and DHA is slow, only a maximum of 15% of ALA (flax seed oil) can convert to EPA and 5%, in any at all, may convert to DHA. Although flax seed has many benefits, it is not recommended as a source of Omega-3 EPA and DHA fatty acids.