Based on some emails I received about my blog post from November 17, I realize that there is a little bit of confusion about the different types of omega-3 fats. I want to clear that up so that readers can make the best informed decision about meeting needs for these compounds.
There are two different type of omega-3 fats in foods. We definitely need one of these and may need the other.
Alpha-linolenic acid (ALA) is a short-chain omega-3 fatty acid that is an essential nutrient. We absolutely need to have some in our diet. It’s provided by just a few plant foods but requirements are so small that it’s easy to get enough. You can meet your entire needs for the day by consuming a teaspoon of flaxseed oil or a tablespoon of canola oil or 3 to 4 walnut halves.
DHA and EPA are the long-chain omega-3 fats that are found in fish oils. Although there is a little bit of EPA in sea vegetables, vegans generally don’t consume these fats at all. While DHA and EPA are not considered essential nutrients (there is no RDA for them), they are linked to some health benefits including reduced risk for heart disease. Low levels of DHA may raise risk for depression and, in older people, cognitive decline.
Even though vegans don’t consume these fats, we do have some in our blood because the body can make DHA and EPA from the essential fat ALA. The problem is that it takes a lot of ALA–maybe more than is actually healthy–and the conversion doesn’t seem to be very efficient. There is some evidence, including the findings from the EPIC-Norfolk study I wrote about, that the conversion is more efficient in vegetarians than in meat-eaters. But even so, vegetarians’ blood levels of EPA and DHA are generally lower than those of people who consume fish.
So, everyone needs to consume some source of ALA no matter what; it’s an essential nutrient. Even if you are taking DHA supplements, you still need ALA in your diet because it has its own set of functions.
And consuming ALA from flaxseed or hemp oil or other foods does not necessarily mean that you’ll end up with optimal DHA levels. Taking DHA supplements from algae is effective in raising levels of both DHA and EPA in the blood (some of the DHA converts back to EPA). But whether or not vegetarians benefit from those higher levels isn’t known.
If you want to know everything in the world about omega-3 fats in vegetarian diets, I recommend the section covering this topic on veganhealth.org.