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HOW SHOULD THE RECOMMENDED DIETARY ALLOWANCES BE REVISED? B Need for Change Voiced by the Scientific and Advocacy Communities SUMMARY OF COMMENTS AND TESTIMONY QUESTION 1: What Has Been the Experience Applying the RDAs in Different Situations, and What Factors Limit Their Usefulness? Invited speakers representing government agencies and industries that rely on the RDAs noted that the RDAs are used to plan and procure food supplies for population subgroups, interpret food consumption records for individuals and populations, establish standards for food assistance programs, evaluate the adequacy of food supplies in meeting nutritional needs, design nutrition education programs, develop new products in industry, and establish guidelines for nutrition labeling of foods. By serving as the independent standards of nutritional adequacy, the RDAs play an important role in determining meals served in hospitals, nursing homes, prisons, publicly run residential care institutions, and other places where the participants' nutritional status and health are likely to be marginal. The RDAs act as independent guideposts for developing nutritional standards for federal food assistance programs and serve to protect the nutritional integrity of these programs. The invited speakers raised concerns about limitations of the RDAs when used for these different applications. These include the incompleteness of the scientific base used to determine the RDAs, uncertainties about the biological variability in requirements that exist among individuals, and limitations that result from the focus on the traditional concern of preventing deficiency disorders. Several other limitations identified were the lack of additional age-specific recommendations for individuals over the age of 51, a group that is
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HOW SHOULD THE RECOMMENDED DIETARY ALLOWANCES BE REVISED? becoming an increasingly larger proportion of the population; lack of sufficient emphasis on the range of appropriate macronutrient intakes; lack of relevance to chronic disease and the concomitant need to address dietary fat, fiber, and some vitamins; lack of information that addresses nutrient needs over the life cycle; little consideration of nutrient interactions; and lack of consideration for varying activity levels. Moreover, since the RDAs build in a margin of safety, some individuals were concerned that actual requirements are overestimated, making it difficult to determine at what levels of intake a population is truly at risk. Several speakers commented that perhaps the RDAs are attempting to fulfill too many purposes. They argued that professionals and the public may be better served by having several levels of dietary allowances established to address different needs and purposes. One suggestion was that more than one set of guidelines be developed, similar to the approach taken by the United Kingdom (U.K.) (COMA, 1991). The U.K. approach includes developing three values for each nutrient: a low value estimating a deficiency state, a value representative of the population's average requirement, and a third value analogous to the current RDA and approximately two standard deviations above the average requirement. Others additionally recommended setting an upper safe level of intake that would be established where undesirable health effects are likely to occur in the population as a whole. Several requested that consideration be given to developing a separate set of RDAs for use in food labeling, while cautioning that frequent changes in the RDAs would pose financial hardships to industry. One individual urged that international harmonization be considered if the FNB were to develop an RDA for food labeling purposes. Throughout the testimony, many individuals emphasized the need for additional documentation to explain the derivation of the numbers and to facilitate their appropriate applications. Additional documentation would describe the state of knowledge concerning the levels of nutrients and food components needed for health promotion and disease prevention, to provide guidance to professionals who are using the RDAs for a variety of applications, and to identify gaps in knowledge so research priorities can be established. A suggestion was made to merge dietary guidelines with the RDAs to promote one consistent message to the public and to provide this information for the public's use in a less scientific and more accessible publication than the traditional RDA text.
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HOW SHOULD THE RECOMMENDED DIETARY ALLOWANCES BE REVISED? QUESTION 2: What New Evidence Would Argue for a Change from the Present Values or a Reexamination of the Evidence? There was general agreement that an RDA committee should be established to review new data available since publication of the tenth edition in 1989. The viewpoints expressed regarding specific revisions can be divided into three areas: recommendations for an increase in an existing RDA, recommendations for a decrease in an existing RDA, and recommendations for establishing a new RDA for a particular nutrient or food component not currently covered. One or more commenters concluded that sufficient data have accumulated that would argue for increasing the RDAs for folic acid, calcium, vitamin D, and the antioxidant vitamins (ascorbic acid and vitamin E) for at least some age and sex categories. The new data they cited indicate a role for folic acid in reducing the risk of neural tube defects, for folic acid and antioxidant vitamins in reducing the risk of some cancers, and for calcium and vitamin D in increasing bone mass accretion among children and adolescents and preventing bone loss in adults. Others expressed the opinion that the RDAs for caloric intake, protein, and iron might be lowered in light of new data. These commenters stated that doubly labeled water and indirect calorimetry experiments indicate that energy requirements among some age groups may be lower than currently estimated. Similarly, it was voiced that protein requirements for children and for adults need to be reviewed. The possible adverse effects of iron as a catalyst for oxyradical formation and facilitator of other oxidation processes were cited as potential justification for lowering the iron RDA for some age and sex categories. Various commenters expressed views that sufficient data were available now to set RDAs for nutrients and food components that are not currently addressed in the tables. These include beta-carotene, omega-3-fatty acids, sodium, choline, dietary fiber, and macronutrients in light of data on their roles in reducing the risk of cancer, cardiovascular disease, and other chronic diseases. Several speakers commented that the recommendations for sodium need to be reviewed; that the interrelationships between sodium and potassium, calcium, and magnesium be studied; and that sodium restriction should be evaluated in terms of safety and effectiveness in preventing hypertension. QUESTION 3: Should Concepts of Reduction of Risk of Chronic Disease Be Included in the Development of Allowances? The majority, though not unanimous, view expressed by speakers and testifiers was that concepts of risk reduction for chronic disease should be
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HOW SHOULD THE RECOMMENDED DIETARY ALLOWANCES BE REVISED? included in developing the RDAs. Several individuals expressed the opinion that when sufficient data are unavailable to establish an RDA but the emerging trend indicates that certain nutrients have physiological or biochemical implications for health, that emerging information should be communicated, and the recommended levels should reflect an adequate and safe range of intake. A small number of commenters argued that the RDAs should remain distinct from dietary guidelines for reducing the risk of chronic disease. They emphasized that the purposes of the RDAs and the dietary guidelines are very different and that there was a less adequate data base for formulating recommended allowances for reducing the risk of chronic disease. The necessity for a nutrient standard for narrower nutritional applications, such as food labeling, also was mentioned. QUESTION 4: How Should Recommended Levels of Intake Be Expressed? In considering how recommended levels of intake should be expressed, the FNB asked whether individual values should be given for different age and sex categories or whether ranges of recommended intakes should be provided, how the ranges should be defined, and whether toxic levels should be included where data are sufficient to establish an upper limit. Most respondents favored ranges rather than a single value because ranges allow differences among individuals and groups, give more recognition to the biological heterogeneity among individuals, and dispel the notion that the numbers recommended represent exact requirements. However, presenting RDAs as ranges would make it complicated to use them in government programs if advice is lacking about what point in the range is appropriate for different applications. Although most commenters favored the use of ranges, they expressed many different opinions about the appropriate reference points to comprise any range. Some favored defining an upper limit for any nutrient as something less than a toxic level, representing the level of intake associated with maximum health promotion. Some favored defining a middle range as the average requirement while others suggested that the midrange of the level be associated with lowest disease risk. Most agreed that the lowest point in the range should represent the level of intake associated with a high risk for deficiency. QUESTION 5: Is Knowledge of Relationships among Nutrients Sufficient to Consider when Establishing the RDAs? Very few comments were received on this question. This lack of response probably reflects the relative lack of knowledge of nutrient interactions for most vitamins, minerals, and food components. Two invited speakers provided
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HOW SHOULD THE RECOMMENDED DIETARY ALLOWANCES BE REVISED? an overview of the state of knowledge of nutrient bioavailability. They were asked to discuss whether available data are sufficient to permit the use of bioavailability algorithms in establishing the RDAs, an approach used with iron in recent RDA editions. These speakers indicated that a similar approach could be considered for several other nutrients where the data base is sufficient. TESTIMONY RELATED TO THE MECHANISM TO ESTABLISH RDAs Several testifiers addressed the mechanism for developing new RDAs. These comments are summarized below: List index nutrients that if consumed in adequate amounts, would ensure the adequate consumption of all other food components. Relinquish the task of revising the RDAs to groups of scientists in a university setting or to professional societies. Create an office in the Department of Health and Human Services to establish a new conceptual basis for the RDAs, revise the RDAs, and facilitate their use by the public. Once this is done, the Assistant Secretary for Health should use health, medical, and nutrition professionals; consumers; and industry representatives to oversee the development of new RDAs. Form expert panels of individuals with specific training and experience to devise a particular nutrient recommendation. Once the RDAs are revised, expend considerable efforts to promote healthful diets to the public and health care providers. Establish an ongoing RDA committee to ensure that the RDAs are current and that major professional users are informed of potential considerations for revisions. Support ongoing efforts to evaluate the needs for revising current RDAs. Praise was given to the proposed method for setting the RDAs and for reaching out to groups of workers expert in various aspects of each nutrient and health factor relative to the establishment of recommendations. Support legislation in the U.S. Congress that would require the FDA to revise the RDAs. Consider supporting the additional fortification of food as a useful way of delivering nutrients to the public. This was proposed to encourage the consumption of wholesome foods to meet nutritional needs rather than promote the use of supplements.
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