Figure 3. Desaturation and Elongation of Essential Fatty Acids. Humans can synthesize longer omega-6 and omega-3 fatty acids from the essential fatty acids LA and ALA through a series of desaturation (addition of a double bond) and elongation (addition of two carbon atoms) reactions. Delta-6 desaturase (FADS2) is considered the rate-limiting enzyme in this metabolic pathway. Retroconversion of DHA to EPA in peroxisomes occurs at low basal rates and following DHA supplementation.
Click the link for an article on why Fish Oil should be your source for Omega-3 and not flax oil. My Dr, Dr. Aukerman, says all the studies with Flax were done with rats. Rats have an extra enzyme that allows them to utilize all the Omega 3 in flax. So it's good for you, if you are a rat.
New research shows fish intake associated with boost to antidepressant response