As part of a low-fat, heart-healthy diet, consumers are hearing the message to include more fish in their diets. Fish and shellfish contain high-quality protein and other important nutrients, including omega-3 fatty acids. These fatty acids help make the blood less "sticky," so it is less likely to form the clots that lead to heart disease. In addition, one type of omega-3 fatty acid, docosahexaenoic acid, is considered essential for the optimal development of an infant’s brain and eyes both during pregnancy and after birth.
Unfortunately, fish and shellfish also harbor methylmercury, a contaminant that if consumed in large enough quantities can actually damage the developing brain and may be linked to the risk of heart attack and sudden death in adults.
Mercury gets into the food supply naturally from the environment, but also and primarily as a result of industrial pollution. As mercury is released into the air, it accumulates in streams and oceans, where bacteria cause chemical changes that transform mercury into toxic methylmercury. Fish absorb methylmercury as they feed in contaminated waters. The risks from mercury in fish and shellfish depend on the amount of fish and shellfish eaten and the levels of mercury in the fish and shellfish.
While nearly all fish contain trace amounts of methylmercury, it is the long-lived, larger fish that feed on other fish that have the highest levels because they’ve had the most time to accumulate it. When we regularly eat fish containing high amounts of methylmercury, it begins to accumulate in our blood streams. Once in our bodies, methylmercury is removed from the body naturally, but it may take over a year for levels to drop significantly.
Mercury in fish is not a new issue. The Food and Drug Administration and the Environmental Protection Agency have long advised women of childbearing age about the connection between fish and methylmercury. This March, however, the advisory was upgraded to include albacore tuna and tuna steaks in the list of fish with high levels of mercury and to further stress the importance of including young children in the list of those who should monitor their fish intake. The new guidelines were issued after a FDA study found levels of mercury in albacore tuna to be three times higher than previously believed.
The new guidelines recommend the following for women who might become pregnant, women who are pregnant or nursing and for young children:
– Shark, swordfish, king mackerel or tilefish should not be eaten because they contain high amounts of mercury.
– Eat up to 12 ounces (two to three meals) a week of a variety of fish and shellfish that are lower in mercury. Because of their increasing mercury levels, albacore ("white) tuna and tuna steaks together should account for no more than 6 of these 12 ounces. Commonly eaten fish that are relatively low in mercury include shrimp, scallops, canned light tuna, salmon, haddock, pollock, trout, crawfish, sardines and catfish.
– Check local advisories about the safety of fish caught by family or friends in local lakes, rivers and coastal areas. If no advisory is available, eat up to 6 ounces per week of fish caught from local waters, but don’t consume any other fish during that week.
For more information about the risks of mercury in fish and shellfish, call the FDA’s food information line toll-free at 1-888-SAFEFOOD or visit FDA’s Food Safety Web site at www.cfsan.fda.gov/seafood1.html. Information about the safety of locally caught fish and shellfish can be found at the Environmental Protection Agency’s Fish Advisory Web site at www.epa.gov/ost/fish or by contacting your local or state Health Department.
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by Pat Kendall, Ph.D., R.D., Food Science and Human Nutrition Specialist, Colorado State University, Cooperative Extension