Although EPA, DHA, and ALA are all long-chain PUFAs, ALA is the shortest of the three. To get a bit more science-y, EPA has 20 carbons and double bonds, DHA has 22 carbons and six double bonds, and ALA has 18 carbons and three double bonds. As these chemical differences indicate, they are three unique fats with unique roles in our physiological health and wellness.
Another difference is availability. ALA is prevalent in our diets and found in plentiful amounts in many plants—including flaxseed, canola oil, olive oil, walnuts, and other tree nuts, according to Chip Lavie, M.D., FACC, FACP, FCCP, medical director of cardiac rehabilitation and prevention at Ochsner Health.
In contrast, EPA and DHA are not widely found in the food supply, nor are these marine omega-3s widely consumed by Americans. And since only a small amount of ALA is converted to EPA and DHA, we're lacking these PUFA MVPs that work overtime for our heart, brain, redox balance, and more.* “Making EPA and DHA from ALA is possible but very inefficient, and achieving optimal omega-3 index levels is nearly impossible with only ALA,” says Harris.