Fish Oil

Fish oil contains heart-healthy omega-3 fatty acids. Many studies find some beneficial effect, especially against heart attacks. But supplements can have adverse effects. A drying oil can be obtained from menhaden, pilchard, sardine and herring. Fish oil should not be confused with fish liver oil. It contains 20% polyunsaturated fatty acids, 30-35% saturated fatty acids, 40-55% monoenoic fatty acids, 7-15% dienoic fatty acids, 3-10% trienoic fatty acids, less than 2% tetraenoic or higher fatty acids.

There is considerable evidence that fish and fish oils are beneficial to heart health, reduce the risk of cancer, and benefit mental health. The "active" components of fish oils are eicosapentaenoic acid (EPA), a polyunsaturated fatty acid with 20 carbon atoms in its backbone, and docosahexaenoic acid (DHA), a polyunsaturated fatty acid with 22 carbon atoms. Both are members of the omega-3 group of essential fatty acids. EPA and DHA are found exclusively in marine animals; fatty fish such as herring, sardines, salmon and fresh tuna are the best sources.

Who should consider taking fish-oil supplements:

  • People who already have coronary artery disease, notably those who have had a heart attack. There is solid evidence that omega-3s can help protect them. Thus, the AHA (the American Heart Association) started recommending 1 gram a day of omega-3s, preferably from fish, for these people, with their doctors’ approval. That’s the amount in a serving of fatty fish, such as 3 ounces of salmon. But most people don’t eat fish every day, and many choose less-fatty fish (it takes 12 ounces of canned tuna or 7 ounces of flounder to supply 1 gram of omega-3s). Moreover, since fish may contain mercury, we advise limiting fish intake to 12 ounces a week, on average. So to get enough omega-3s without going overboard on fish, people with heart disease should consider taking fish-oil supplements on days when they don’t eat fish.
  • Those with high triglycerides. These fats in the blood increase the risk of heart disease. It’s well known that omega-3s help lower triglycerides. The AHA recommends 2 to 4 grams a day from supplements for people with high triglycerides, but only under the care of a physician.
  • Those with rheumatoid arthritis, psoriasis, or other auto-immune disorders. Omega-3s may help relieve the inflammatory symptoms of such auto-immune diseases by suppressing the immune response. Thus, they can help reduce the joint pain and swelling of rheumatoid arthritis. The Arthritis Foundation says the supplements are worth trying. Clinical studies suggest about 3 grams of omega-3s a day.

If fish oil is so great, why shouldn’t everyone take supplements?

  • The decreased ability of the blood to clot, which helps prevent heart attacks, has a negative side, notably an increased risk of hemorrhagic stroke. People with bleeding disorders, those taking anticoagulants, and those with uncontrolled hypertension should not take fish oil supplements.
  • Large doses of fish oil may suppress the immune system. Thus, supplements may be risky for those with weakened immune systems. What’s a "large dose"? One definition is 3 grams or more a day, but no one really knows what the cutoff point is.
  • Large doses can increase glucose levels in people with diabetes.
  • Large doses can cause nausea, diarrhea, belching, and a bad taste in the mouth.
  • The supplements may contain contaminants and may not contain the labeled dose. A recent test by Consumer Reports of top-selling supplements was reassuring on both counts, even for the least expensive brands, but that doesn’t mean that the next batches will be okay, or that other brands on the market are. Last year a test by ConsumerLab.com found no detectable levels of mercury in 20 fish-oil supplements, but did find that some brands didn’t contain the labeled amounts of omega-3s.

It is rare for a major health group like the AHA to recommend any dietary supplement. But remember, its advice concerns the treatment of specific diseases. For everyone else, two or three small servings of fish a week is still the way to go. Fish may be more beneficial than the supplements because it contains other important nutrients, some potentially cardio-protective. And fish can take the place of meat, which is usually high in saturated fat and thus bad for the heart.