ALA, EPA, and DHA: three omega-3s
ALA, EPA, and DHA all belong to the omega-3 family, but they are distinct fatty acids. Their names encode different chain lengths and double-bond patterns, and they occur in different foods. Treating “omega-3” as one interchangeable number can hide those differences.
Same family, different structures
Alpha-linolenic acid (ALA) has 18 carbon atoms. Eicosapentaenoic acid (EPA) has 20, and docosahexaenoic acid (DHA) has 22. All are polyunsaturated omega-3 fatty acids, but EPA and DHA are described as long-chain omega-3s because of their larger carbon chains.
Their different structures give them different roles in the body. A food’s ALA content therefore tells you something different from its EPA or DHA content.
Where they come from
ALA is found in plant foods and oils, including flaxseed, chia, walnuts, soybean oil, and canola oil. EPA and DHA are found in fish, fish oils, and krill oils; algal oils can provide DHA and sometimes EPA. The amounts in fish vary with species, environment, and feed, so “fish” is not a single composition value.
When comparing foods or oils, check which fatty acids the amount includes. “Total omega-3” can conceal very different proportions of ALA, EPA and DHA.
Conversion is limited
The body can convert ALA to EPA and then DHA, but NIH ODS describes the conversion as very limited, with reported rates below 15%. As a result, the amount of ALA in a meal should not be presented as if it were the same amount of EPA or DHA.
The U.S. Food and Nutrition Board’s adult adequate intakes apply to ALA; it has not set specific intake recommendations for EPA or DHA. References also differ between jurisdictions, so the authority and fatty acid should be named together.
References
Source-checked educational draft. Human editorial review pending.
NIH Office of Dietary SupplementsOmega-3 Fatty Acids - Health Professional Fact SheetSource accessed 2026-09-05European Food Safety AuthorityScientific Opinion on Dietary Reference Values for fats, including saturated fatty acids, polyunsaturated fatty acids, monounsaturated fatty acids, trans fatty acids, and cholesterolSource accessed 2026-09-05