Fish oil labels: finding the EPA and DHA that matter

Fish oil weight is not omega-3 weight

The large number on the front of a fish oil bottle is usually the weight of the oil in each softgel. Only part of that oil is EPA and DHA, the two omega-3 fatty acids people take fish oil for. The rest is other fats.

The NIH describes a typical fish oil supplement as 1,000 mg of fish oil providing 180 mg of EPA and 120 mg of DHA, or about 30% of the oil. Concentrated products can provide much more per softgel. When comparing products, compare EPA plus DHA, not softgel size or total fish oil.

Per softgel vs. per serving

Check the serving size line before reading any amount. Some labels list amounts for one softgel, others for a serving of two or three. The directions may also call for more than one serving a day.

The figure that reflects your intake is the amount per serving multiplied by the servings you take. A label can look modest per softgel and add up quickly, or look large per serving because the serving is three softgels.

How the amounts compare with food and limits

There is no official recommended daily amount for EPA or DHA. The adequate intakes set by the Institute of Medicine cover ALA, the plant omega-3: 1.6 g a day for adult men and 1.1 g for adult women. Your body converts only small amounts of ALA into EPA and DHA.

For safety, FDA has concluded that supplements providing no more than 5 g a day of EPA and DHA combined are safe when used as recommended, and that supplement labels should not recommend more than 2 g a day.

What the label cannot tell you: freshness

Omega-3 fatty acids oxidize, or go stale, over time. Oxidation is measured with three lab values: peroxide value, p-anisidine value, and TOTOX, which combines the two. The industry group GOED sets voluntary limits of a peroxide value below 5 meq O₂/kg, a p-anisidine value below 20, and a TOTOX below 26.

Products do not always meet those limits. In a 2020 study of 44 fish oil supplements sold in the UAE, 40.9% exceeded the peroxide limit and 27.3% exceeded the TOTOX limit. The authors cite an earlier U.S. survey in which 27% exceeded the peroxide limit.

A Supplement Facts panel lists amounts, not freshness. Freshness only shows up if a certificate of analysis includes an oxidation test, and many do not. We say on our transparency page whether our current lot's document includes one. For our current lot, it does not.

Side effects and interactions

The NIH lists commonly reported side effects of omega-3 supplements as usually mild: unpleasant taste, bad breath, heartburn, nausea, digestive discomfort, diarrhea, headache, and odorous sweat. Taking softgels with meals is a common way people reduce aftertaste.

Fish oil might prolong clotting time. If you take a blood thinner such as warfarin, or have a procedure scheduled, talk with your clinician before starting it.