Compound-specific isotope analysis reveals no retroconversion of DHA to EPA but

substantial conversion of EPA to DHA following supplementation: a randomized control trial

https://academic.oup.com/ajcn/article/110/4/823/5519526

I’m not really familiar with the nomenclature and measuring methods but the logic sounds sound and it is a clever way to utilize naturally occurring isotopes to show conversions paths as opposed to labeling the dha and epa which is what I thought they were doing initially (and if it were would have made it easier to understand but probably more dangerous for the participants.)

In any case it raises the questions of

1  whether the proportions of epa and dha are really important as long as the epa is sufficient and

2  if all those patented epa formulations really maintain their epa identity in the body.  I doubt that conversion to dha was checked for since it was heretofore not believed to occur.