The health benefits of dietary EPA and DHA are vast, but not everyone consumes fish and other seafood that contains them. For these individuals, supplementation plays an important role doing exactly what it is supposed to do – supplement a dietary deficit. However, there is still much controversy over the most bioavailable form of EPA and DHA in supplements.

This is because EPA and DHA can be packaged in different ways, such as bound to phospholipids (PL), bound to triglycerides (TG), or as ethyl esters (EE). Around 95% of dietary fat and most of the storage fat within the body are TG, with most the rest being PL. However, PLs are the primary component of cell membranes, so it is easy to see why some may argue that this form is superior for EPA and DHA supplementation. In contrast to these naturally occurring forms of delivery, EEs are synthetically created by reacting EPA and DHA with alcohol so as to selectively concentrate the fatty acids and allow for more concentrated fish oil supplements.

To put an end to the confusion, Yurko-Mauro et al conducted a double-blind, randomized, parallel-arm controlled trial comparing the oral bioavailability of a 1.3 gram per day dose of EPA+DHA supplied primarily as krill oil (40% PL) or fish oil TG or EE. Ultimately, sixty six healthy adults with a low habitual consumption of EPA and DHA consumed their respective supplements daily for 4 weeks.

By the end of the intervention, there was a clear trend (p=0.052) for greater bioavailability of EPA and DHA in the blood plasma with krill oil then fish oil TG then fish oil EE. A similar observation can be seen for EPA specifically, although this was not close to being statistically significant. On the other hand, there was a significant advantage of both krill oil and TG fish oil (without difference between one-another) compared to EE fish oil when looking specifically at the bioavailability of DHA.

If we look specifically at red blood cells (RBCs), which serve as a proxy for long-term intake and are what is analyzed for tests such as the omega-index, there was no significant difference among any of the forms, although both krill oil and TG fish oils were about 14% greater than the EE fish oil.

The title of this study alludes to the conclusions of the authors, which is that there is no difference among the different types of fish oil – and they are technically correct according to their statistical methods and the fact that the overall difference in EPA and DHA blood plasma concentrations failed to reach statistical significance. Yet, the results did show a significant superiority of krill oil and TG-bound fish oil to EE-bound fish oils for DHA concentrations, not to mention that if the researchers accepted an extra 0.02% chance of being wrong, the overall results would have become significant.

This paper and the authors’ hard-ass stance serve as a great example of why you cannot always trust the title of a publication and need to look at the data to form a conclusion. As it turns out, four of the six authors, all of which participated in designing the study, collecting and interpreting the data, and writing the manuscript, are employees of DSM Nutrition Products, which sells fish oil supplements. Actually, two of its supplements were the TG and EE fish oils used in this experiment, while the krill oil was that of a competitor.

Regardless, do these results suggest you should be taking krill oil rather than fish oil? No, owed in no small part to the fact that krill oil composition in various commercial products varies widely in phospholipid content from approximately 19-81%, thus making it impossible to know what exactly you are purchasing (the product in the current study was about 40%). Speaking of which, krill oil usually sells for a premium in comparison to fish oil and it stands to reason that the differences in bioavailability would be compensated for by simply taking more EPA and DHA from the less bioavailable fish oil supplements.

So, I guess the bottom line is that phospholipid-bound EPA and DHA are going to be the most bioavailable overall, but that triglyceride-bound EPA and DHA is not much different when looking at DHA specifically or when looking at RBCs. However, EE fish oils are the worst overall, which may be compensated for by their higher concentration in supplements for similar prices.