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Seafood Choices carefully explores the decision-making process for selecting seafood by assessing the evidence on availability of specific nutrients (compared to other food sources) to obtain the greatest nutritional benefits. The book prioritizes the potential for adverse health effects from both naturally occurring and introduced toxicants in seafood; assesses evidence on the availability of specific nutrients in seafood compared to other food sources; determines the impact of modifying food choices to reduce intake of toxicants on nutrient intake and nutritional status within the U.S. population; develops a decision path for U.S. consumers to weigh their seafood choices to obtain nutritional benefits balanced against exposure risks; and identifies data gaps and recommendations for future research.
The information provided in this book will benefit food technologists, food manufacturers, nutritionists, and those involved in health professions making nutritional recommendations.
BALANCING BENEFITS AND RISKS
Copyright © 2007 National Academy of Sciences
All right reserved.
Seafood (referring in this report to all commercially obtained fish, shellfish, and mollusks, both marine and freshwater) is a nutrient-rich food source that is widely available to most Americans. It is a good source of high-quality protein, is low in saturated fat, and is rich in many micronutrients. Seafood is often also a rich source of the preformed long-chain polyunsaturated omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are synthesized in limited amounts by the human body from alpha-linolenic acid (ALA), a fatty acid found in several vegetable, nut, and seed oils (e.g., walnut and flaxseed oils). In the past several years, research has implicated seafood, particularly its contribution of EPA and DHA, in various health benefits identified for the developing fetus and infants, and also for adults, including those at risk for cardiovascular disease. Contamination of aquatic food sources, however, whether by naturally-occurring or introduced toxicants, is a concern for US consumers because of adverse health effects that have been associated with exposure to such compounds. Methylmercury can accumulate in the lean tissue of seafood, particularly large, predatory species such asswordfish, certain shark, tilefish, and king mackerel. Lipophilic compounds such as dioxins and polychlorinated biphenyls (PCBs) can be found in the fatty tissue of some fish. High levels of particular microbial pathogens may be present during certain seasons in various geographic areas, which can compromise the safety of products commonly eaten raw, such as oysters. Additionally, some population groups have been identified as being at greater risk from exposure to certain contaminants in seafood.
In consideration of these issues, the US Department of Commerce, National Oceanic and Atmospheric Administration (NOAA) asked the Institute of Medicine (IOM) of the National Academies to examine relationships between benefits and risks associated with seafood consumption to help consumers make informed choices. The expert committee was asked to prioritize the potential for adverse health effects from both naturally occurring and introduced toxicants in seafood, assess evidence on availability of specific nutrients in seafood compared to other food sources, determine the impact of modifying food choices to reduce intake of naturally occurring and introduced toxicants on nutrient intake and nutritional status within the US population, develop a decision path for US consumers to weigh their seafood choices to obtain nutritional benefits balanced against exposure risks, and identify data gaps and recommend future research.
The committee concentrated primarily on seafood derived from marine (saltwater) sources and included freshwater fisheries when appropriate to the discussion. Further, the committee recognized that these sources vary greatly in their level of contamination depending on local conditions, and that individual states have issued a large number of advisories based on assessment of local conditions. Although the committee was not asked to consider questions or make recommendations about environmental concerns related to seafood, it recognizes that the impact of changes in seafood production, harvesting, and processing have important environmental consequences.
To address the task of assessing benefit-risk trade-offs, the committee took a three-step approach. The steps that framed this analytical approach were: (1) analysis and balancing of the benefits and risks (including attention to characteristics that distinguish target populations as well as substitution predictions); (2) analysis of consumer perceptions and decision-making (understanding decision contexts and their variability, and assessing consumers' behavior regarding how they perceive and make choices); and (3) design and evaluation of the decision support program itself (including format and structure of information, media, and combination of communication products and processes). The aim of the analysis in step 1 is to assess the overall effect of seafood selections rather than the assessment of reduction in a specific risk or enhancement of a specific benefit.
ANALYSIS OF THE BALANCING OF BENEFITS AND RISKS OF SEAFOOD CONSUMPTION
The scientific assessment and balancing of the benefits and risks associated with seafood consumption is a complex task. Diverse evidence, of varying levels of completeness and uncertainty, on different types of benefits and risks must be combined to carry out the assessment required as a first step in designing consumer guidance. In light of the uncertainty in the available scientific information associated with both nutrient intake and contaminant exposure from seafood, no summary metric adequately captures the complexity of seafood benefit/risk trade-offs. Thus, the committee developed a four-part qualitative protocol adapted from previous work (IOM, 2003) to evaluate and balance benefits and risks. Following the protocol, the committee considered consumption patterns of seafood; the scope of the benefits and risks associated with different patterns of consumption for the population as a whole and, if appropriate, for specific target populations; and changes in benefits and risks associated with changes in consumption patterns. It then balanced the benefits and risks to come to specific guidance for healthy consumption for the population as a whole, and, as appropriate, for specific target populations.
Consumption of Seafood in the United States
Seafood consumption has increased over the past century, reaching a level of more than 16 pounds per person per year in 2003. The ten types of seafood consumed in the greatest quantities among the US general population (from highest to lowest) are shrimp, canned tuna, salmon, pollock, catfish, tilapia, crab, cod, clams, and flatfish (e.g., flounder and sole). The nation's seafood supply is changing, however, and this may have a significant impact on seafood choices in the future. The preference among consumers for marine types of seafood is leading to supply deficits, and seafood produced by aquaculture is replacing captured supplies for several of these types.
While seafood is recognized as a primary source of the omega-3 long-chain polyunsaturated fatty acids EPA and DHA, not all seafood is rich in these fatty acids. Among types of seafood, shrimp and canned light tuna are the two most commonly consumed, and they are not especially high in EPA and DHA. Eggs and chicken, although not particularly rich sources, may contribute to the EPA and DHA content of the US diet because of their frequent consumption. Relative to other foods in the meat, poultry, fish, and eggs group, however, seafood is generally lower in saturated fatty acids and higher in EPA, DHA, and selenium, all of which have been associated with health benefits.
1. Average quantities of seafood consumed by the general US population, and by several specific population groups, are below levels suggested by many authoritative groups, including levels recommended by the American Heart Association for cardiovascular disease prevention; and
2. For many ethnic and geographic subgroups, there are insufficient data to characterize the intake levels of seafood, EPA, DHA, and other dietary constituents, and to assess the variability of those intakes.
Benefits Associated with Nutrients from Seafood
The high nutritional quality of seafood makes it an important component of a healthy diet. While protein is an important macronutrient in the diet, most Americans already consume enough and do not need to increase their intake. Fats and oils are also part of a healthful diet, but the type and amount of fat can be important-for example, with regard to cardiovascular disease. Many Americans consume greater than recommended amounts of saturated fat as well as cholesterol from high-fat protein foods such as beef and pork. Many seafood selections are lower in total and saturated fats and cholesterol than some more frequently selected animal protein foods such as fatty cuts of beef, pork, and poultry, and are equivalent in amount of fat to some leaner cuts of meat. Since it is lower in saturated fats, however, by substituting seafood more often for other animal foods, consumers can decrease their overall intake of both total and saturated fats while retaining the nutritional quality of other protein food choices.
Seafood is also a primary source of EPA and DHA in the American diet. The contribution of these nutrients to improving health and reducing risk for certain chronic diseases in adults has not been completely elucidated. There is evidence, however, to suggest there are benefits to the developing infant, such as increasing length of gestation, improved visual acuity, and improved cognitive development. In addition, there is evidence to support an overall benefit to the general population for reduced risk of heart disease among those who eat seafood compared to those who do not, and there may be benefits from consuming EPA and DHA for adults at risk for coronary heart disease.
1. Seafood is a nutrient-rich food that makes a positive contribution to a healthful diet. It is a good source of protein, and relative to other protein foods, e.g., meat, poultry, and eggs, is generally lower in saturated fatty acids and higher in the omega-3 fatty acids EPA and DHA as well as selenium;
2. The evidence to support benefits to pregnancy outcome in females who consume seafood or fish-oil supplements as part of their diet during pregnancy is derived largely from observational studies. Clinical trials and epidemiological studies have also shown an association between increased duration of gestation and intake of seafood or fish-oil supplements. Evidence that the infants and children of mothers who consume seafood or EPA/DHA supplements during pregnancy and/or lactation may have improved developmental outcomes is also supported largely by observational studies;
3. Observational evidence suggests that increased seafood consumption is associated with a decreased risk of cardiovascular deaths and cardiovascular events in the general population. Evidence is insufficient to assess if this association is mediated through an increase in EPA and DHA consumption and/or a decrease in saturated fat consumption and/or other correlates of seafood consumption;
4. Evidence is inconsistent for protection against further cardiovascular events in individuals with a history of myocardial infarction from consumption of EPA/DHA-containing seafood or fish-oil supplements. The protection evidenced by population (observational) studies has not been consistently observed in randomized clinical trials; and
5. Evidence for a benefit associated with seafood consumption or fish-oil supplements on blood pressure, stroke, cancer, asthma, type II diabetes, or Alzheimer's disease is inconclusive. Whereas observational studies have suggested a protective role of EPA/DHA for each of these diseases, supportive evidence from randomized clinical trials is either nonexistent or inconclusive.
Risks Associated with Seafood
The safety of seafood in the US has increased in recent decades, although there are still a number of chemical and microbial hazards that are present in seafood. Whether a contaminant poses a health risk to consumers depends on the amount present in the food and the potential outcome from exposure. Consumers are exposed to a complex mixture of dietary and non-dietary contaminants. However, most studies of the risks associated with seafood focus on one contaminant at a time rather than a mixture. The extent to which such coexposures might affect the toxicity of seafoodborne contaminants is largely unknown. Similarly, few data are available on the extent to which beneficial components of seafood, such as selenium, might mitigate the risks associated with seafoodborne contaminants. The evidence reviewed indicates that the levels of different contaminants in seafood depend on several factors such as species, size, location, age, and feed source. Levels of some contaminants in seafood vary substantially due to their geographic localization; areas of highest variation tend to be mostly freshwater.
Consumption of aquatic foods is the major route of human exposure to methylmercury (MeHg). The seafood choices a consumer makes and the frequency with which different species are consumed are thus important determinants of methylmercury intake. Exposure to MeHg among US consumers in general is a concern because there is uncertainty about the potential for subtle adverse health outcomes. Since the most sensitive subgroup of the population to MeHg exposure is the developing fetus, intake recommendations are developed for and directed to the pregnant woman rather than to the general population.
Persistent organic pollutants (POPs), including dioxins and PCBs, can be found in the fatty tissue of all animal-derived foods, including seafood. Exposure to these compounds among the general population has been decreasing in recent decades. The greatest concern is for population groups exposed to POPs in seafood obtained through cultural, subsistence, or recreational fishing, because of reliance on fish from locations that may pose a greater risk.
In contrast to heavy metal contaminants and POPs, the number of reported illnesses from seafoodborne microbial contaminants has remained steady over the past several decades. Exposure to vibrio and norovirus infections is still a concern, however, because they continue to be associated with consumption of raw molluscan shellfish. Strategies for minimizing the risk of seafoodborne illnesses are, to some extent, hazard-specific, but overall include avoiding types of seafood identified as being more likely to contain certain contaminants, and following general food safety guidelines, which include proper cooking.
1. Levels of contaminants in seafood depend on several factors, including species, size, harvest location, age, and composition of feed. MeHg is the seafoodborne contaminant for which the most exposure and toxicity data are available; levels of MeHg in seafood have not changed substantially in recent decades. Exposure to dioxins and PCBs varies by location and vulnerable subgroups (e.g., some American Indian/Alaskan Native groups living near contaminated waters) may be at increased risk. Microbial illness from seafood is acute, persistent, and a potentially serious risk, although incidence of illness has not increased in recent decades.
2. Considerable uncertainties are associated with estimates of the health risks to the general population from exposures to methylmercury and persistent organic pollutants at levels present in commercially obtained seafood. The available evidence to assess risks to the US population is incomplete and useful to only a limited extent.
3. Consumers are exposed to a complex mixture of dietary and non-dietary contaminants whereas most studies of risks associated with seafood focus on a single contaminant.
Balancing Benefits and Risks
From its review of consumption, benefits, and risks, the committee recommends that:
Recommendation 1: Dietary advice to the general population from federal agencies should emphasize that seafood is a component of a healthy diet, particularly as it can displace other protein sources higher in saturated fat. Seafood can favorably substitute for other high biologic value protein sources while often improving the overall nutrient profile of the diet.
Recommendation 2: Although advice from federal agencies should also support inclusion of seafood in the diets of pregnant females or those who may become pregnant, any consumption advice should stay within federal advisories for specific seafood types and state advisories for locally caught fish.
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2 CONSUMPTION PATTERNS AND COMPOSITION OF SEAFOOD....................30
3 HEALTH BENEFITS ASSOCIATED WITH NUTRIENTS IN SEAFOOD....................67
4 HEALTH RISKS ASSOCIATED WITH SEAFOOD CONSUMPTION....................121
5 ANALYSIS OF THE BALANCING OF BENEFITS AND RISKS OF SEAFOOD CONSUMPTION....................195
6 UNDERSTANDING CONSUMER DECISION MAKING AS THE BASIS FOR THE DESIGN OF CONSUMER GUIDANCE....................217
7 BALANCING CHOICES: SUPPORTING CONSUMER SEAFOOD CONSUMPTION DECISIONS....................248
APPENDIXES A Glossary and Supplementary Information....................275
B Data Tables....................297
C Tables and Scenarios....................683
D Open Session and Workshop Agendas....................687
E Committee Member Biographical Sketches....................691