Omega-3s Part 1—Basics

by Jack Norris, RD • Last updated June 2012

More Information on Omega-3s



There are three important omega-3 fatty acids:

α-linolenic acid (ALA)

ALA is a short-chain fatty acid. It’s found in small amounts in animal flesh, in very small amounts in a variety of plant products, and in relatively large amounts in soy, walnuts, canola oil, camelina oil, and in flax, hemp, and chia seeds and their oils. The human body cannot make its own ALA—it’s an essential fatty acid that must be obtained through the diet.

Eicosapentaenoic acid (EPA)

EPA is a long-chain fatty acid. It’s found in large amounts in fatty fish, in small amounts in eggs, and in very small amounts in seaweed that can be concentrated into supplements. Some EPA is converted into other molecules that can reduce blood clotting, inflammation, blood pressure, and cholesterol.

Docosahexaenoic acid (DHA)

DHA is a long-chain fatty acid. It’s found in large amounts in fatty fish, in small amounts in eggs, and in very small amounts in seaweed that can be concentrated into supplements. DHA is a major component of the gray matter of the brain, and is also found in the retina, testis, sperm, and cell membranes.

The body can convert ALA into EPA, and EPA into DHA. ALA is efficiently converted to EPA, but it may require large amounts of ALA to produce optimal amounts of DHA.

Health Benefits

The American Heart Association (AHA) recommends that adults eat at least two servings of fatty fish a week. The AHA says that people with coronary artery disease may want to talk to their doctor about supplements, especially for people with high triglycerides.

However, they also state that “Some types of fish may contain high levels of mercury, PCBs (polychlorinated biphenyls), dioxins and other environmental contaminants,” providing a possible advantage to seaweed-based omega-3 supplements.

Aside from fish-based omega-3s, an ALA intake of about 2 g per day has been consistently associated with a modest lowering of heart disease risk.

There’s evidence that EPA and/or DHA supplementation may improve depression and cognition, particularly in infants, children, and older adults, although the results of clinical trials have been mixed. Especially in the case of older vegetarians and vegans, there’s a concern that an omega-3 deficiency could cause cognitive problems and omega-3 supplementation is recommended.

Omega-3 Status of Vegetarians and Vegans

Vegetarians and vegans have been shown in many studies to have lower blood levels of EPA and DHA than meat eaters. It’s not known if lower blood DHA levels reflect lower levels in other tissues in vegetarians and vegans.

Because EPA reduces blood clotting, one way to figure out if vegetarians and vegans are getting enough EPA is to compare the blood clotting parameters of vegetarians and vegans to omnivores. Two studies have done this and found the differences to be minimal.

Vegetarians and vegans already have about a one-quarter lower risk of heart disease than regular meat-eaters and on average have lower triglyceride levels—it’s not clear that EPA or DHA supplementation will further reduce their risk.

In terms of depression and cognition, there’s been no research on omega-3s and vegetarians and vegans, but there are anecdotal reports of some older vegan men with very low DHA levels and cognitive problems, so there’s reason to be prudent regarding DHA in older vegetarians and vegans, especially men.

Improving Omega-3 Status in Vegetarians and Vegans

Traditionally, vegetarians and vegans have been encouraged to raise EPA and DHA levels by increasing ALA and decreasing the short-chain omega-6 fatty acid linoleic acid (LA) that can interfere with omega-3 conversion.

An ideal ratio of omega-6 to omega-3 in the diet is thought to be about 3:1 to 4:1. Vegans tend to have a ratio of 10:1 to 15:1 compared to a ratio of 6:1 to 10:1 for omnivores.

Unfortunately, there are no long-term studies looking at the EPA and DHA levels in vegetarians and vegans who follow the recommendations to increase ALA and limit LA, though research on omnivores shows that 3–4 g of ALA per day can increase DHA levels.

There are now many companies offering vegan DHA supplements made from seaweed, and some include EPA. If you’re getting plenty of ALA, you shouldn’t need a supplement with EPA.

Too much omega-3 can result in bleeding and bruising. If you bleed or bruise easily, consult a health professional before significantly increasing your omega-3 intake.

Daily Needs

For recommendations that will provide vegetarians and vegans with a similar omega-3 fatty acid status to fish eaters, please see Daily Needs.

More Information

See Fish and Cardiovascular Disease for an analysis of the benefits of eating fish or taking fish oil supplements for the general public and how that impacts a vegetarian or vegan diet.

The Linus Pauling Institute at Oregon State University provides an in-depth review of omega-3s and heart disease in Essential Fatty Acids.

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