The fragmented information that consumers receive about the nutritional value and health risks associated with fish and shellfish can result in confusion or misperceptions about this food source, says a new report by the Institute of Medicine.
The report reviews the scientific evidence on seafood's benefits and risks and offers examples of how such information might be presented in a more coherent way to the public. It calls for federal agencies to partner with state, local, and private groups to develop new informational tools and test them with consumers to make sure they work.
"Consumers need better guidance on making seafood choices," said Malden C. Nesheim, professor emeritus and provost emeritus, Cornell University, Ithaca, N.Y., and chair of the committee that wrote the report. "The committee's approach to balancing the benefits and risks brings this information together in a coordinated way that applies to all population groups. Our model offers a foundation upon which agencies can develop advice that presents information in a user-friendly way and allows consumers to weigh all the relevant details and make well-informed choices."
Much of the evidence on seafood's health benefits and risks is preliminary or insufficient, the committee found. Reliable data on the distribution of some contaminants is lacking, and there is little evidence on how beneficial effects of seafood might counteract some of the risks from contaminants. Evidence suggesting that people who have suffered heart attacks can reduce their risk of future heart attacks by eating seafood is weaker than previously thought, the committee concluded. It is also not clear whether consuming seafood might reduce people's risks for diabetes, cancer, Alzheimer's disease, or other ailments.
However, the committee confirmed that eating fish and shellfish may reduce people's overall risk for developing heart disease. It is not certain whether this is because substituting the lean protein of seafood for fatty cuts of meat reduces consumers' intake of saturated fat and cholesterol or because of the protective effects of omega-3 fatty acids, which are found in relatively high amounts in many fish species. Americans generally consume too much saturated fat and cholesterol and too little of "good fats" such as the omega-3 fatty acids EPA and DHA in fish. The report also found evidence that maternal consumption of omega-3 fatty acids through seafood can contribute to vision and cognitive development in infants and lengthen the duration of gestation.
Seafood is the major source of human exposure to methylmercury, a contaminant that accumulates in the muscle of animals over time. Because evidence suggests that methylmercury can disrupt neurodevelopment in the fetus, the report supports current recommendations that women who are pregnant or wish to become pregnant avoid consumption of lean, predatory fish such as swordfish, shark, king mackerel, and tilefish, and limit their consumption of albacore, or "white," tuna. Other potential risks associated with seafood are exposure to persistent organic pollutants such as dioxin and PCBs -- though there is not clear evidence on the adverse effects associated with these compounds -- and microbial infections, which are contracted mainly through the consumption of raw or undercooked fish and shellfish.
The report supports current dietary guidelines and seafood advisories. However, the committee's interpretation of the risks and benefits (see Box S-1 below) differs in that it consolidates information on both risks and benefits for sensitive population groups and addresses all segments of the population. And it does not support giving those with a history of heart disease advice different from that given to the general population.
Most people can gain nutritional benefits from seafood while minimizing their risk of exposure to contaminants by selecting fish and shellfish in amounts that fall within current dietary guidelines, the report says. Because seafood supplies and cultivation practices change constantly, it would be difficult for federal agencies to develop a list of "good fish" and "bad fish" that would not become obsolete in a short time. However, the benefits and risks for broad categories of seafood are relatively consistent:
• Lean fish are good sources of protein, are low in saturated fat and cholesterol, and provide moderate amounts of omega-3 fatty acids. Predatory fish with long life spans -- such as swordfish, shark, and tilefish -- contain levels of methylmercury that are too high for pregnant and breast-feeding women.
• Fatty fish such as salmon are good sources of protein and provide the highest amounts of omega-3 fatty acids. They also contain higher levels of saturated fat and cholesterol and can accumulate higher amounts of pollutants such as dioxin and PCB, depending upon the source. Their methylmercury burden is lower than that of many lean fish.
• Shellfish and crustaceans are good sources of protein and low in saturated fat, although some contain moderate amounts of cholesterol. They present the greatest risk of microbial infection if eaten raw.
• For all seafood categories, levels of contaminants such as dioxin and PCBs in commercially obtained fish generally do not pose health risks when consumed in amounts recommended by federal agencies. These contaminants tend to be geographically specific problems. State advisories are intended to alert the public about contaminated fish and shellfish from regional and local sources.
Helping consumers to make seafood choices requires giving them information to weigh the benefits and risks of different fish and shellfish varieties and to understand the trade-offs of substituting seafood for other protein sources. For example, healthy young women who are or wish to become pregnant should avoid certain types of fish that are higher in methylmercury, but this need not be a concern for men. Choosing a serving of salmon instead of a serving of fatty beef will lower a woman's intake of saturated fat and cholesterol and boost her intake of omega-3 fatty acids, but it also will reduce her iron intake and may increase her exposure to methylmercury slightly. Selecting light canned tuna instead of salmon will decrease her exposure to dioxin, but it may increase her exposure to methylmercury and reduce her intake of omega-3 fatty acids.
The committee presented a variety of tools that could be used to inform consumers, including a series of questions designed to provide advice tailored to their specific needs. This way of arriving at a decision should be used as a basis for developing additional decision-support tools and other consumer guidance, the report says. The committee also developed sample graphs illustrating how levels of omega-3 fatty acids and methylmercury vary in different types of fish. These graphics may present this information to consumers more effectively than plain text or numbers, but their design and wording have not been tested among consumers. Testing through focus groups or other empirical means should be an integral part of efforts to develop new seafood communications tools and strategies to make sure they are clear and do not lead to unexpected negative results, the report says. For example, previous advice to Native Alaskans to reduce their intake of seafood and marine mammals -- intended to reduce their exposure to pollutants -- inadvertently resulted in many people eating greater amounts of high-calorie, low-nutrient processed foods.
The committee did not explore environmental factors that also may affect consumers' seafood choices. It did not endorse any specific sources of seafood, but rather showed what the evidence says about the nutrient and contaminant content of various types.
The study was sponsored by the National Oceanic and Atmospheric Administration with additional support from the U.S. Food and Drug Administration. Established in 1970 under the charter of the National Academy of Sciences, the Institute of Medicine provides independent, objective, evidence-based advice to policymakers, health professionals, the private sector, and the public. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies. A committee roster follows.
Pre-publication copies of SEAFOOD CHOICES: BALANCING BENEFITS AND RISKS are available from the National Academies Press; tel. 202-334-3313 or 1-800-624-6242 or on the Internet at www.nap.edu.
