There continues to be much confusion among vegans about the differences between the two types of omega-3 fats. If you take supplements of DHA (or DHA and EPA), do you still need to eat flaxseeds? And if you are eating flaxseeds, do you need those DHA supplements?
The short answer is that you definitely need to include foods like flaxseeds that provide essential omega-3 fats and you may need the DHA supplements.
Flaxseeds and a handful of other plant foods provide an omega-3 fat called alpha-linolenic acid or ALA which is an essential nutrient. This means it is absolutely necessary in your diet. Best sources for vegans are flaxseed and flax oil, chia seeds, hempseed oil, walnuts or walnut oil, canola oil, and full fat soyfoods. You can check these charts on the Vegan Health website to see ALA requirements and food sources of this nutrient.
The other omega-3 fats are DHA and EPA, typically found in fatty fish, and to a much lesser extent in some sea vegetables. They are not considered essential nutrients because humans can synthesize these fats from ALA. Whether we can make enough for optimal health is a big question, though. Vegans have lower blood levels of these fats than people who eat fish, but how much this matters remains unclear. The jury is still out on the health benefits of DHA and EPA intake. They may help protect against heart disease as well as dementia and depression, but the findings are conflicting. It’s possible that low DHA and EPA levels are part of the explanation for why findings on heart disease risk in vegans are less impressive than expected. But we just don’t know. The good news is that if you choose to take supplements of DHA and EPA (and I do), there are vegan sources derived from algae.
Note that some experts have advised limiting certain other fat-rich foods as a way to enhance conversion of ALA to DHA and EPA. Specifically, keeping your diet low in another fat, called linoleic acid (LA), can free up the enzyme needed to convert ALA to DHA and EPA. There has been lots of discussion on manipulating the ratio of LA and ALA in vegan diets. In the 2020 edition of Vegan for Life, we didn’t recommend that approach. The exact ratio of the two fats—LA and ALA—for maximizing conversion isn’t known. It’s also not known whether diets very low in LA (which is also an essential fat) are healthy. It makes more sense to focus on eating enough ALA—the essential fat in flaxseeds and walnuts—and to consider a supplement of DHA and EPA.
The important thing to remember, though, is that the two types of omega-3 fats are not interchangeable. Whether or not you’re taking supplements of DHA and EPA, you still need a source of ALA, like flaxseeds. And, even with a good source of ALA in your diet, you may benefit from supplements of DHA and EPA, especially if you’re at risk for heart disease or depression.