Find the Right Fish Oil
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It's common knowledge: Fish oil works. Doctors agree that its essential fatty acids can help prevent heart disease and may ward off diabetes, arthritis, obesity, and other illnesses. And with the majority of Americans deficient in them, you're probably not meeting your needs by eating salmon or fortified eggs alone.

But it's easy to be overwhelmed in the store by all sorts of liquids and pills, from different sources and in myriad concentrations. Flax, krill, or mackerel? EPA, DHA, or ALA? Before you pick up something that may not have the right components or come from the best sources, figure out what you need in an omega-3. Here are four pointers to find high-quality fish oil.

1. Look for DHA and EPA
The strongest proven benefits of omega-3 fatty acids are improved cardiovascular health and lowered triglycerides — unhealthy fats in the blood linked to heart disease. These advantages have been traced primarily to only two types of omega-3s: DHA and EPA, which are found in algae and fatty fish like anchovies and salmon. The first thing to look for in a supplement, then, is that it contains both DHA and EPA. Find a product with a serving size of at least one gram total — the daily dose recommended by most experts — and don't worry about the exact ratio of EPA to DHA, as there is no agreement yet on what that should be. Because EPA and DHA make up only about 30 percent of most fish oil — the rest is usually other fatty acids with fewer established health benefits — look for a product with as high a concentration of these as possible. If you're concerned about burping fish — a common complaint with fish oil — opt for an enteric-coated pill, which will release lower in your digestive tract.

2. Don't Bother With ALA
ALA, a plant form of omega-3, often shows up in supplements as flaxseed oil. It's not as potent as EPA or DHA, and because the body is inefficient at converting ALA into these, it's best to skip it altogether. Also avoid supplements with omega-6 fatty acids — Americans already consume too much of them, in the form of vegetable oils in chips, salad dressings, cakes, and other foods. In excess, omega-6s can promote inflammation and may contribute to cardiovascular disease and cancer. Pass on supplements with omega-9s — a fancy term for the fats found in olive and canola oils. You're probably already eating plenty, plus your body can produce it from unsaturated fats found in vegetable oils. Finally, don't bother with GLA, often listed as evening primrose, or DGLA. Both are expensive and haven't been shown to have benefits beyond possibly improving the sheen of skin and hair.

3. Choose Algae Oil for Sustainability
If you're worried about depleting marine resources, choose a supplement made from algae grown on farms. Oil extracted from small fish like anchovies is usually more sustainable: Smaller species mature faster and are often caught in schools, lessening the chance of other fish being mistakenly captured. Krill is more controversial because it's a food source for many animals and its numbers are being threatened by global warming and human demand.

4. Don't Worry About Mercury
You don't have to worry about contaminants like mercury, lead, or PCBs making their way into fish-oil supplements. Contrary to popular belief, contamination risk is low. "Fish oil is one of the few good news stories from a contamination perspective," says Dr. Tod Cooperman, president of ConsumerLab.com, which conducts independent testing of omega-3 supplements. "We've looked at hundreds of products and have not found any mercury, [and] the levels of PCBs are so trace that they're nothing to be concerned about."