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ACSM'S Health & Fitness Journal:
doi: 10.1249/FIT.0b013e3181bcd765
DEPARTMENTS: You Asked For It: Question Authority

You Asked For It: Question Authority

Nieman, David C. Dr.P.H., FACSM

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David C. Nieman, Dr.P.H., FACSM, is professor and director of the Human Performance Laboratory, Appalachian State University, in Boone, North Carolina; an active researcher; and author of several textbooks on health and fitness. Email your questions to niemandc@appstate.edu.

Q: I have heard that omega-3 fatty acids are good for your heart, but I am confused about the best way to safely include them in my diet. Should I use supplements or include more fish? Also, can regular use of fish oil supplements help me recover better from hard exercise bouts?

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A: For heart health, I recommend that you aim for at least two fish dishes per week. Fish oil supplements can be considered if you do not eat fish and are at elevated risk for heart disease. In contrast, the best evidence does not support a role for fish oil supplements in countering exercise-induced inflammation and soreness.

Nearly 40 years ago, researchers first reported that heart disease was rare in Eskimos because of their large intake of fish (2). Other cultures with high fish consumption, such as the Japanese, also experienced low heart disease death rates. Clinical studies revealed that fish such as salmon and albacore tuna had high levels of a unique type of fat called omega-3 fatty acids. During the past three decades, researchers discovered multiple health benefits from consuming omega-3 fatty acids, prompting the American Heart Association and other organizations to establish guidelines urging people to eat more fish and omega-3 fatty acids for the prevention of cardiovascular diseases (4). High intake of omega-3 fatty acids also has been linked to reduced risk of depression, bone loss, diabetes, certain cancers, and Alzheimer disease (6).

Omega-3 fatty acids are a unique type of polyunsaturated fat, and there are three major types: α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Fish oil contains both EPA and DHA, whereas some nuts (English walnuts) and vegetable oils (canola, soybean, flaxseed/linseed, olive) contain ALA (10). ALA must come from the diet because it cannot be made by the body and is, therefore, considered an essential fatty acid.

American adults consume approximately 1,600 mg of omega-3 fatty acids each day, of which 90% comes from ALA and only 10% from EPA and DHA. The reason for low intakes of EPA and DHA is that few people regularly consume oily fish, the richest dietary source of these fatty acids.

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The reluctance of U.S. adults to increase fish intake and concerns over heavy metal accumulation in fish have accelerated interest in botanical sources of omega-3 fatty acids, especially flaxseed, chia seed, and certain types of plant oils (10). Plant omega-3 fatty acids (ALA) are abundant and readily available and are often contained in foods that are high in dietary fiber and other healthy components. The cardioprotective effect of ALA in humans, however, is uncertain, and studies differ widely regarding influences on blood lipid profiles and measures of inflammation. The best evidence shows that a large proportion of ALA is used as fuel for metabolism, and that enzymatic conversion to EPA and DHA is relatively inefficient in humans (1). Thus, most experts recommend that EPA and DHA from fish or fish oil be included in the diet.

Recommendations for EPA and DHA vary, but in general, most organizations recommend a range of 300 to 1,000 mg/day from fatty fish and supplements. For healthy adults with no history of heart disease, the American Heart Association recommends eating fish at least two times per week (4). In particular, fatty fish high in EPA and DHA is recommended, such as anchovies, bluefish, carp, catfish, halibut, herring, lake trout, mackerel, pompano, salmon, striped sea bass, tuna (albacore), and whitefish. One 3-oz serving of wild Atlantic salmon provides about 1,500 mg of EPA and DHA, and a 3-oz serving of canned white tuna provides 700 mg (see Table).

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TABLE Levels of Merc...
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The American Heart Association also recommends that those with coronary heart disease eat 1,000 mg/day of EPA plus DHA from oily fish or supplements (4). The Food and Drug Administration (FDA) recommends that consumers not exceed 3,000 mg/day of EPA and DHA, with no more than 2,000 mg/day from a dietary supplement.

Ingestion of omega-3 fat from fish has impressive benefits for the heart and reduces the risk of heart attacks (4,9). One or two servings of cold-water fish per week reduce risk of coronary heart disease by 36% (4,9). Exactly how fish oils help the heart is not completely understood but may be related to the ability of EPA and DHA to stabilize heart cells, lower blood triglycerides, and prevent blood clots from forming. The ALA from plants such as flaxseed, soybeans, and walnuts may help reduce deaths from heart disease but to a much lesser extent than fish oil (9).

The FDA classifies intake of omega-3 fatty acids from fish as GRAS (generally regarded as safe). Potential safety issues with eating fish or the use of EPA and DHA supplements exist, but these are generally regarded as minor. Some types of fish may contain significant levels of methylmercury, polychlorinated biphenyls, dioxins, and other environmental contaminants. Levels of these substances are generally highest in older, larger, predatory fish and marine mammals (e.g., shark, swordfish, and king mackerel) and should be avoided (see Table). Children and pregnant women are advised by the FDA to avoid eating those fish with the potential for the highest level of mercury contamination. Potential exposure to some contaminants can be reduced by removing the skin and surface fat from these fish before cooking. Eating a variety of fish will help minimize any potentially adverse effects caused by environmental pollutants. Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.

The fish oil industry has successfully improved the quality of fish oils on the market. An independent test of 42 fish oils on the U.S. market by www.consumerlab.com found that all of the products exceeded safety standards for potential contaminants.

Should fish oil supplements be used by athletes to help counter the effects of hard workouts and competitions? Transient inflammation and immune dysfunction are part of the normal human response to prolonged and intense exercise. Fish oil has been touted for its anti-inflammatory and immune-boosting benefits, and thus it makes sense that fish oil is held up as a dietary aid to help athletes recover from hard exercise (3).

One fish oil researcher has reasoned that most athletes need 1 to 2 g of EPA and DHA each day to counter excessive oxygen radical formation, inflammation, and trauma from high-intensity exercise (7). Two recent studies, however, using excellent research designs have failed to demonstrate that 6 weeks of supplementation with 2.4 to 3.6 g/day of EPA and DHA helps counter the inflammation, muscle soreness, oxidative stress, and immune dysfunction caused by heavy exertion in endurance athletes (5,8).

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In general, fish and shellfish are an important part of a healthy diet and contain high-quality protein and other essential nutrients, are low in saturated fat, and contain omega-3 fatty acids. A well-balanced diet that includes a variety of fish and shellfish, or EPA and DHA supplements, can contribute to heart health and perhaps lowered risk for other chronic diseases. However, high doses of EPA and DHA do not confer additional benefits for the endurance athlete seeking relief from the inflammation and pain of heavy training.

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References

1. Arterburn LM, Hall EB, Oken H. Distribution, interconversion, and dose response of n-3 fatty acids in humans. Am J Clin Nutr. 2006;83(6 Suppl):1467S-76S.

2. Bang HO, Dyerberg J, Sinclair HM. The composition of the Eskimo food in northwestern Greenland. Am J Clin Nutr. 1980;33:2657-61.

3. Calder PC. Immunomodulation by omega-3 fatty acids. Prostaglandins Leukot Essent Fatty Acids. 2007;77:327-35.

4. Lichtenstein AH, Appel LJ, Brands M, et al. Diet and lifestyle recommendations revision 2006: A scientific statement from the American Heart Association nutrition committee. Circulation. 2006;114:82-96.

5. Nieman DC, Henson DA, McAnulty SR, Jin F, Maxwell KR. N-3 polyunsaturated fatty acids do not alter immune and inflammation measures in endurance athletes. Int J Sports Nutr Exerc Metab. 2009;(in press).

6. Riediger ND, Othman RA, Suh M, Moghadasian MH. A systemic review of the roles of n-3 fatty acids in health and disease. J Am Diet Assoc. 2009;109:668-79.

7. Simopoulos AP. Omega-3 fatty acids and athletics. Curr Sports Med Rep. 2007;6:230-6.

8. Toft AD, Thorn M, Ostrowski K, et al. N-3 polyunsaturated fatty acids do not affect cytokine response to strenuous exercise. J Appl Physiol. 2000;89:2401-6.

9. Wang C, Harris WS, Chung M, et al. N-3 fatty acids from fish or fish-oil supplements, but not alpha-linolenic acid, benefit cardiovascular disease outcomes in primary- and secondary-prevention studies: A systematic review. Am J Clin Nutr. 2006;84:5-17.

10. Whelan J, Rust C. Innovative dietary sources of n-3 fatty acids. Ann Rev Nutr. 2006;26:75-103.

© 2009 American College of Sports Medicine

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