The fish oil folks will tell you that the human body doesn't efficiently convert EPA and DHA from seed based Omega 3 fatty acids. They've got studies to back them up.
But it doesn't make any sense. If the only efficient way to get Omega 3 metabolytes was by ingesting them directly from cold water fish, then wouldn't the human population long ago have moved to the shores of the northern oceans for basic survival? Instead we find people groups living, and thriving, on the vast plains of every continent ( perhaps excepting Australia ).
A very recent study out of Deakin University in Victoria, Australia, sheds a little light on the possible explanation. The folks who designed this study were looking for a more efficient way to perform and measure in vitro ( in the lab ) experiments involving Omega 3 bioconversion. Along the way, they made some observations that were not directly what they were looking for, but interesting nonetheless.
One of the observations established that “rather than the existence of a single rate- limiting step affecting the overall pathway, a combination of different level of efficiency in each enzymatic step is responsible for the production of n-3 LC-PUFA [ Omega 3 long chain polyunsaturated fatty acids – that is, EPA, DHA, etc. ] biosynthesis.”
They also found a lot more metabolytes outside the cells they were culturing, in the medium itself, at the end of the process. They were not surprised by this, because the liver does the conversion to pass the metabolytes into the blood stream for the body to utilize, but it was an “Oh, right...” moment.
In other words, what you find depends on where you look and how long you're willing to wait for the outcome. DHA, which is an extremely important metabolyte, apparently takes up to five days to produce. Most studies, they suggest, aren't looking long enough, and so are underreporting the bioconversion results.
What it all means is that we need to go back and look at the studies denigrating in vivo EPA and DHA conversion from seed based alpha linolenic acid, the methodologies, and the timeframes. I have a sneaking suspicion we'll find that when they calculated out how well the body converts Omega 3 oils to what it needs, they weren't sticking around long enough to find the finished product.
Ramez Alhazzaa1*, Andrew J. Sinclair2, Giovanni M. Turchini
School of Life and Environmental Sciences, Deakin University, Victoria, Australia, 2 School of Medicine, Deakin University, Victoria, Australia