Experts from Purdue University claim consumers should fish for information before buying seafood to make sure the benefits outweigh the risks.
"We know that eating fish – which are full of protein and omega-3 fatty acids – promotes good health," said Charles Santerre, a foods and nutrition associate professor who specializes in chemical contaminants in food. "At the same time, we know that some fish, including commercial fish, can be harmful. The consumer – especially a woman in her childbearing years –needs to be discerning.
"A woman should carefully choose the fish she eats today to protect her baby tomorrow."
Fish, such as swordfish, shark, king mackerel and tilefish, can contain high levels of methylmercury that, if eaten regularly, can harm the developing nervous system of a fetus or infant. Santerre said these fish should be avoided by pregnant women, nursing mothers and young children.
"Ironically, these fish are popular, especially with people in the high-income bracket," he said.
Polychlorinated biphenyls (PCBs), sometimes found in fish, also pose a threat.
"It takes six years to rid the body of PCBs and one year for mercury," Santerre said.
Other fish, such as salmon, which is high in long-chain omega-3 fatty acids, such as DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), should be a regular component of a woman's diet.
"Salmon is an ideal source for long-chain omega-3 fatty acids, which are necessary for brain development in babies and cardiovascular health in adults. At the same time, some other kinds of fish that contain a large amount of healthy fats also can have high levels of brain toxins," he said.
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Santerre said pregnant and nursing women can get the greatest benefit from fish by complying with a few recommendations.
The safest seafoods are farmed and wild salmon, along with oysters, shrimp, farm-raised channel catfish, farm-raised rainbow trout, flounder, perch, tialpia, clams, scallops and red swamp crayfish. These have the lowest level of mercury and can be eaten more than once a week. Canned tuna, crab, cod, mahi-mahi, haddock, whitefish, herring and spiny lobster have slightly higher levels of mercury and should be eaten no more than one meal per week.
Some seafood should be limited to just one meal a month: tuna steaks, red snapper, orange roughy, pollack, halibut, northern lobster, marlin, moonfish, saltwater bass, wild trout, bluefish, grouper, croaker and sablefish. So, if a pregnant woman has a meal of red snapper, she should not eat grouper for at least another month, Santerre said.
"Consumers, especially a pregnant or nursing woman, should also be aware of the source of some food," Santerre said. "If she is not sure whether the commercial fish is farmed or wild, she should ask her grocer or waiter. Wild and farmed salmon are both generally safe because wild salmon is from Alaska, which has cleaner bodies of water. However, wild trout is not as safe as farmed trout, because wild trout is generally from landlocked waters. Most trout in stores is farm-raised."
Santerre said the good news is that not only are salmon full of the best kind of fatty acids and low in contaminants, they also are becoming more affordable due to increased production in fish farming.
The role of these polyunsaturated essential fatty acids in the diet also has gained new recognition. The National Academy of Sciences Food and Nutrition Board's Dietary Reference Intake Committee recently established macronutrient dietary intake recommendations for omega-3 fatty acids. They recommend .13 to .14 grams per day of EPA plus DHA for pregnant and nursing women.
For example, eight ounces of salmon per week provides four times the recommended amount of DHA and EPA. Eight ounces of canned light tuna (in water) only provides 60 percent of the recommended amounts, while the same amount of canned white tuna provides twice the recommended level. Catfish only provides 40 percent of these lipids but is low in contaminants.
Jay Burgess, associate professor of foods and nutrition at Purdue, said everyone can benefit from an adequate diet of omega-3 fatty acids, but adequate amounts are especially important for pregnant or nursing women.
"For some women, their breast milk omega-3 fatty acid content may not be sufficient," said Burgess, whose area of expertise is fatty acid analysis and metabolism. "It is a good idea to increase the amount of omega-3 in the mother's system so that when she nurses her milk has the optimal level of fatty acids. Fish is a way to do that, but there is this dilemma about toxins in fish. So how do we help mothers make this decision?"
"By applying food contaminant data from the Food and Drug Administration to Environmental Protection Agency methylmercury and PCB recommended limits, we have a more user-friendly guide for consumers to learn how to select fish," Santerre said.