Does the form of omega-3 you choose matter?

Ethyl esters are the most widely sold form in supplements, but also the least well absorbed. They must first be broken down by enzymes from the pancreas, and those enzymes only work properly when you eat fat alongside them. If you take them with a low-fat meal, absorption drops even further.

The free fatty acid form (sometimes referred to as omega-3 carboxylic acids) shows the highest absorption in short-term studies. You do not necessarily need to take them with a fatty meal, and they do not need to be converted first by digestive enzymes. At clinical doses of 2 to 4 grams per day, this form reduced triglycerides in people with markedly elevated levels by 26 to 31 percent. However, this has been studied as a prescription medicine, not as a standalone supplement.

A newer, pre-digested form called monoacylglycerol showed absorption in one human study that was comparably high to the free fatty acid form, and clearly higher than ethyl esters. The triglyceride form, as found in ordinary fish oil, falls in between.

Krill oil and omega-3 from fish roe contain the fatty acids in phospholipid form. Animal research points to higher absorption for this form, but in humans the results are too inconsistent to make firm statements about it.

The most important caveat in all of this: the acute absorption differences seen in short-term studies do not always translate into measurably higher blood levels during months of daily use. Whether the choice of form actually matters for your health in the long term is therefore uncertain. Added to this, the research in this area has serious methodological shortcomings: different measurement methods, varying doses and groups that are too small. Firm conclusions are therefore hard to draw.