Harvard Health Letter

By the way, doctor: Can you give me some advice about omega-3s?

Q. I am confused about omega-3 fats. Are the different types equally good for you?

A. There are three main types to keep track of: eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and alpha-linolenic acid (ALA). EPA and DHA are found mainly in fish, so they're sometimes called marine omega-3s. ALA is found in plant-based foods, such as flaxseed, walnuts, and canola and soybean oils.

So far, the evidence for EPA and DHA having health benefits is more extensive than for ALA. Studies have shown that EPA and DHA offer some measure of protection against heart attacks and strokes. EPA and DHA also have anti-inflammatory effects that may be useful in preventing or treating conditions like rheumatoid arthritis and inflammatory bowel disease. Some well-designed studies of ALA are under way, but right now there just aren't enough data to be confident about ALA having the same effects as EPA and DHA. And there's reason for doubting whether it does. The body converts ALA to EPA and then to DHA, but that happens only in small amounts. If you're aiming to increase your omega-3 intake to accomplish all the things that omega-3s are thought to do, increasing the amount of fish you eat is probably the best way to go. That said, flaxseed and the other ALA-rich oils may still be a healthful choice, if you are using them to replace trans or saturated fat.

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