News Coverage
The dilemma: How much seafood to eat for health benefits without getting too many contaminants?
Published August 5, 2003
Choosing what fish to put on your plate seems to get more complicated by the day.
Health questions range from how much seafood to eat to get the benefit of desirable omega-3 fatty acids to whether that fish contains harmful levels of environmental contaminants. Throw in ecological concerns like overfishing and pollution from farming operations, and it's the would-be fish eater who's in a stew.
Perhaps the most troubling issue for many is finding a balance between the benefits of eating seafood and the potential risks. There's little question that eating seafood is good for you. It's low in saturated fats and a good source of protein. Many fish are rich in omega-3, a fat that reduces the risk of cardiovascular disease and is believed to boost brain function in developing infants.
Yet chemicals such as methylmercury and polychlorinated biphenyls, or PCBs, are present in some fish and may pose health hazards, depending on how much is eaten. Various advocacy groups, as well as health associations and federal agencies, have weighed in with advice on what's safe to eat, and how much.
While all agree on the benefits of eating seafood and encourage people to continue doing so, they disagree on what to eat, how much and how often. And they worry that telling people to avoid certain fish will drive them away from fish altogether, and to less healthy foods. Everyone agrees that eating a balanced diet that includes a variety of fish is optimal.
"Fish is good for you," says David Acheson, chief medical officer of the federal Food and Drug Administration. But, he adds, "not all fish are equal."
Much of the disagreement in recent months has focused on two of the three most popular fish in the United States, canned tuna and salmon.
The FDA is considering changes to its mercury advisory, which counsels pregnant women, nursing mothers and young children to avoid eating shark, tilefish, king mackerel or swordfish. Those species often contain high levels of mercury, which can damage the nervous systems of unborn babies and may pose risks to young children, too. Pregnant women can safely eat 12 ounces of cooked fish of other species each week, the advisory says.
Some environmental groups say that canned tuna should be added to the advisory list. Although it contains lower levels of mercury than any fish on the list, it's eaten much more frequently, and mercury builds up in the body over time. One advocacy organization, the Environmental Working Group, advises pregnant women to eat no more than one 6-ounce can of tuna per month.
"The rub is that it's important for women to get seafood while they're pregnant, because of the nutrients that are important to fetal brain development," says Jane Houlihan, vice president for research of the Environmental Working Group.
For now, it appears unlikely that the FDA will add canned tuna to its "don't eat" list. But as the agency draws up changes to its mercury warning, it is considering clarifying the advice that pregnant women should eat a variety of fish, Acheson says. Eating different species spreads out the risk of consuming environmental contaminants.
"Don't eat all the same type," Acheson says. "Eat a meal of canned tuna and eat a meal of something else. That would be a variety. It could be shrimp; it could be salmon."
Fish pick up contaminants through what they eat --- either smaller fish, commercial food or aquatic plants that can contain pollutants such as methylmercury and PCBs. PCBs, banned in the 1970s, were used as insulators in transformers. They accumulate in animal fat and can be found in a variety of foods, such as beef, full-fat dairy products and chicken with skin, as well as fatty fish like salmon. Large, older predator fish are most likely to contain high levels of mercury, which also builds up over time.
Because it takes many years for the body to shed dioxin and dioxin-like compounds, which include some PCBs, the National Academy of Sciences advises that young girls and women of childbearing age eat foods low in animal fats. PCBs and dioxin have been linked to increased risk of cancer as well as harmful effects on the brains of developing infants.
Two federal agencies regulate fish. The FDA sets contaminant limits for commercial fish, and the Environmental Protection Agency issues guidelines for recreational, freshwater fish. The EPA guidelines assume that anglers are likely to return to the same spot and catch the same kind of fish, so they are often more restrictive than the FDA rules, which assume that consumers are eating a variety of fish from difference sources. Those differences can be confusing.
The Environmental Working Group is asking the FDA to impose more stringent standards for allowable PCB levels in salmon, to match EPA guidelines. A report released last week by the group questioned the safety of farmed salmon. It said that seven of the 10 fish it tested contained levels of PCBs high enough to pose a health risk if eaten too frequently. The report advised people to eat wild or canned salmon instead, or to limit farmed salmon to no more than 8 ounces a month.
Yet salmon is one of the best sources of omega-3s, and all the fish tested fell well within FDA limits. Compared with wild salmon, farmed is available year-round and is usually cheaper. For now, most health groups and government agencies advise keeping it on the plate.
"If people restrict their intake of salmon to once or twice a week, then the benefit from the omega-3s is going to outweigh whatever deleterious effect the environmental contamination may have," says Robert Lawrence, chairman of the National Academy of Sciences committee that examined dioxin levels in food and a professor of preventive medicine at the Bloomberg School of Public Health at Johns Hopkins University.
PCB levels in the diet have decreased 90 percent over the past 30 years, says Terry Troxell, director of the FDA's Office of Plants and Dairy Foods and Beverages.
"FDA's advice is not to alter consumption of salmon or other fish," Troxell says. "We need to balance the importance of fish in nutrition, which is extremely important, with the small traces of PCBs that are still left in the environment and which we are still working hard to minimize."
The American Heart Association recommends eating 3 ounces of cooked fish at least twice a week to gain the heart-healthy effects of omega-3s. The benefits to middle-aged and older men, and post-menopausal women, far outweigh any risk of environmental contamination when the fish meet guidelines set by the FDA and the U.S. Environmental Protection Agency, according to the association. Children and pregnant or nursing women, who have a lower risk of heart disease but are more susceptible to contaminants in fish, should be cautious about what fish they eat, the AHA says.
The omega-3s in fish are considered especially beneficial, but there are alternative sources, such as walnuts, ground flaxseed and canola oil.
"Omega-3s are not the only things in your diet that are going to be heart-healthy and heart-protective," says Chris Rosenbloom, a nutrition professor at Georgia State University. "The whole diet is important. Following the recommendations of the American Heart Association to get two fish meals a week is still a good recommendation."
WHO SAYS WHAT ABOUT EATING FISH
The most specific advice on how much fish to eat, and which fish to avoid, concerns pregnant women, nursing mothers and young children. They're considered most at risk from the effects of methylmercury. Here's what various federal and state agencies advise, depending on whether you're buying fish from a store or restaurant or eating fish caught by a friend or family member.
* FDA, for fish sold in supermarkets and restaurants: Don't eat shark, swordfish, king mackerel or tilefish. Eat up to 12 ounces a week of other types of cooked fish, making sure to choose a variety: shellfish, canned fish, smaller ocean fish or farm-raised fish. For FDA test results on mercury in many species of commercial seafood, go to www.cfsan.fda.gov/[tilde ]frf/sea-mehg.html.
* EPA, for recreational, freshwater fish: Limit consumption to 6 ounces of cooked seafood a week for women or 2 ounces for young children. If you've already eaten the FDA-recommended limit of 12 ounces of cooked, commercial fish that week, don't eat any fish caught by friends or family members. www.epa.gov/mercury/fish.htm.
* Georgia Department of Natural Resources, on recreational, freshwater fish: In general, it's best to eat smaller fish like bream and crappie than larger ones such as striped or large-mouth bass, which have higher levels of mercury. Recommendations vary depending on where the fish is caught; some of the largest fish should be eaten no more than once a month, but many smaller ones are limited to once a week or carry no restrictions. The DNR has an extensive testing program for fish; for more information, including advisories by species for specific rivers and lakes, go to georgiawildlife.dnr.state.ga.us/content/printversion.asp?txtDocument=32.;
TOP 10 FISH AND SHELLFISH CONSUMED IN THE UNITED STATES
................. Mercury level*..........Omega-3 fatty acids
............. (in parts per million).. (grams per 3-oz. serving)
Canned tuna........... 0.17..................0.26-0.73
Shrimp..............Not detectable............. 0.27
Pollock............... 0.20................... 0.46
Salmon..............Not detectable............0.68-1.83
Cod................... 0.19..................0.13-0.24
Catfish............... 0.07..................0.15-0.20
Clams............. Not detectable............. 0.24
Flounder or sole........0.04................... 0.43
Crabs................0.09-0.18................0.34-0.40
Scallops................0.05................... 0.17
* Fish with levels of 1 ppm or higher should be avoided by pregnant women and young children.