Does the form of omega-3 you choose actually matter?

The form in which you take omega-3 affects how well your body absorbs it. The worst-absorbed form is the ethyl ester, which is found in most cheap fish oil supplements. Your intestines can only process that form after pancreatic juices have broken it down, and that works much better when you eat fat with your meal.

The free fatty acid form (also called the carboxylic acid form) is the best absorbed of all tested forms. It does not need to be converted first and can also be taken on an empty stomach. In patients with severely elevated blood fats, this form reduced triglyceride levels by 26 to 31 percent at two to four grams per day. That is a clinically relevant effect. The monoacylglycerol form also appears to be better absorbed than ethyl esters, at least at higher doses. That finding comes from one human study, so the evidence for it is thinner.

Krill oil and some fish products contain omega-3 in the phospholipid form. Animal research suggests that this form is more bioavailable than the standard triglyceride form, but studies in humans do not produce a consistent picture. Direct comparisons are difficult because the studies have been designed in very different ways.

Here comes the big caveat: better absorption in short-term studies does not automatically mean greater health benefit in the long term. There is still very little research demonstrating that the differences in absorption also translate into long-term effects on your health. Moreover, two large reviews point out that the existing studies are poorly comparable with one another, due to varying measurement methods and dosages. The ranking order (free fatty acids above triglycerides above ethyl esters) is plausible, but a firm conclusion about 'the best form' cannot yet be drawn.

Omega-3 from fatty fish meanwhile remains the best-supported means of protecting your heart, particularly if you already have cardiovascular problems. If you want to choose supplements, the free fatty acid form and the triglyceride form (recognisable as 're-esterified triglyceride' on the label) have a better absorption basis than the cheaper ethyl ester form.