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Omega-3 in fish: How eating fish helps your heart

How much fish should you eat?

For adults, at least two servings of omega-3-rich fish a week are recommended. A serving size is 3 ounces (85 grams), or about the size of a deck of cards. Women who are pregnant or plan to become pregnant and children under age 12 should limit the amount of fish they eat because they're most susceptible to the potential effects of toxins in fish.

Does mercury contamination outweigh the health benefits of eating fish?

The risk of getting too much mercury or other contaminants from fish is generally outweighed by the health benefits that omega-3 fatty acids have. The main types of toxins in fish are mercury, dioxins and polychlorinated biphenyls (PCBs). The amount of toxins depends on the type of fish and where it's caught.

Mercury occurs naturally in small amounts in the environment. But industrial pollution can produce mercury that accumulates in lakes, rivers and oceans, which turns up in the food fish eat. When fish eat this food, mercury builds up in the bodies of the fish.

Large fish that are higher in the food chain — such as shark, tilefish, swordfish and king mackerel — tend to have higher levels of mercury than do smaller fish. Larger fish eat the smaller fish, gaining higher concentrations of the toxin. The longer a fish lives, the larger it grows and the more mercury it can collect.

Pay attention to the type of fish you eat, how much you eat, and other information such as state advisories. Each state issues advisories regarding the safe amount of locally caught fish that can be consumed.

Should anyone avoid eating fish because of the concerns over mercury or other contaminants?

If you eat enough fish containing mercury, the toxin can accumulate in your body. It can take weeks, months or even a year for your body to remove these toxins. Mercury is particularly harmful to the development of the brain and nervous system of unborn children and young children. For most adults, however, it's unlikely that mercury would cause any health concerns.

Still, the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) recommend that these groups limit the amount of fish they eat:

  • Women who are pregnant or trying to become pregnant
  • Breast-feeding mothers
  • Children under age 12

Pregnant women, breast-feeding mothers and children can still get the heart-health benefits of fish by eating fish that's typically low in mercury, such as salmon, and limiting the amount they eat to:

  • No more than 12 ounces (340 grams) of fish in total a week
  • No more than 6 ounces (170 grams) of canned tuna a week
  • No amount of any fish that's typically high in mercury (shark, swordfish, king mackerel and tilefish)

Can you get the same heart-health benefits by eating other foods that contain omega-3 fatty acids, or by taking omega-3 fatty acid supplements?

The evidence is stronger for the benefits of eating fish rich in omega-3 fatty acids than for using supplements. However, people who have heart disease may benefit from supplements of omega-3 fatty acids and should discuss this with their doctors.

Other nonfish food options that do contain some omega-3 fatty acids include flaxseed, flaxseed oil, walnuts, canola oil, soybeans and soybean oil. However, similar to supplements, the evidence of heart-healthy benefits from eating these foods isn't as strong as it is from eating fish.

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References
  1. Fish and omega-3 fatty acids. American Heart Association. http://www.americanheart.org/presenter.jhtml?identifier=4632. Accessed Oct. 7, 2010.
  2. Chattipakron N, et al. Cardiac mortality is associated with low levels of omega-3 and omega-6 fatty acids in the heart of cadavers with a history of coronary heart disease. Nutrition Research. 2009;29:696.
  3. Levitan EB, et al. Fish consumption, marine omega-3 fatty acids, and incidence of heart failure: A population-based prospective study of middle-aged and elderly men. European Heart Journal. 2009;30:1495.
  4. Farzaneh-Far R, et al. Association of marine omega-3 fatty acid levels with telomeric aging in patients with coronary heart disease. Journal of the American Medical Association. 2010;303:250.
  5. Weaver KL, et al. The content of favorable and unfavorable polyunsaturated fatty acids found in commonly eaten fish. Journal of the American Dietetic Association. 2008;108:1178.
  6. Hanwell HEC, et al. Acute fish oil and soy isoflavone supplementation increase postprandial serum (n-3) polyunsaturated fatty acids and isoflavones but do not affect triacylglycerols or biomarkers of oxidative stress in overweight and obese hypertriglyceridemic men. Journal of Nutrition. 2009;139:1128.
  7. What you need to know about mercury in fish and shellfish. U.S. Food and Drug Administration and Environmental Protection Agency. http://www.epa.gov/waterscience/fish/files/MethylmercuryBrochure.pdf. Accessed Oct. 7, 2010.
  8. Philibert A, et al. Fish intake and serum fatty acid profiles from freshwater fish. American Journal of Clinical Nutrition. 2006;84:1299.
  9. Cole DW, et al. Aquaculture: Environmental, toxicological and health issues. International Journal of Hygiene and Environmental Health. 2009;212:369.
HB00087 Dec. 21, 2010

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