How Should the Recommended Dietary Allowances be Revised? (1994)

When the FNB began considering whether the RDAs should be revised, it recognized the need to increase the participatory process. The FNB is gathering information and opinions about the need for revising the RDAs through four mechanisms—(1) prepared talks from researchers invited to participate in a symposium held in Washington, D.C., June 28–29, 1993; (2) oral testimony delivered during the subsequent open hearing; (3) written testimony; and (4) participation in meetings sponsored by other organizations. The opportunity to comment at the symposium and hearing was advertised, and 25 individuals and organizations provided oral testimony and 19 submitted written testimony (see Appendix A). The information gleaned from the conference symposium and public hearing is summarized in Appendix B. This testimony is organized according to the five questions posed that formed the basis for the symposium. The appendix closes with a list of opinions presented that pertain to the process itself. The FNB has reviewed all written and oral comments. These will remain part of the data base the FNB is developing to include in further deliberations.

Last June's symposium and public hearing provided a forum for scientists, advocates, and involved professionals to present the FNB with their viewpoints on issues pertaining to the future of the RDAs. The FNB reviewed the information and developed three general conclusions from it:

1. Sufficient new knowledge has accumulated for selected nutrients, especially energy and several vitamins and minerals, that supports a review of the current RDAs.

2. Reduction in the risk of chronic disease is a concept that should be included in the formulation of future RDAs where sufficient data for efficacy and safety exist.

3. Serious consideration must be given to developing a new format for future RDAs.

The FNB believes that the basic purpose of the RDAs remains valid, that is, “to provide standards to serve as a goal for good nutrition ” (NRC, 1941). Given the research on which RDAs are based, RDAs are meant to be applied to groups of healthy people and not individuals. They are therefore set at levels that exceed the needs of most people to encompass the individual variability in nutrient requirements. In practice, however, most nutritionists would translate the purpose of the RDAs to be the levels of essential nutrients that healthy individuals should consume on average over a period of time to ensure adequate and safe nutrient intakes. One task of a new RDA committee will be to provide practitioners and interested laypersons with guidance on the appropriate ways in which RDAs might be used to evaluate the nutrient needs of individuals.

If no change were to be made in the basic purpose of the RDAs, the FNB would plan to revise RDAs for individual nutrients as the body of scientific evidence accumulates. In this way, specific chapters could be revised and widely disseminated along with an updated table, but the entire text would be revised less frequently than has been the case in the past.

The FNB members feel strongly that future RDA documents need to provide more detail about the derivation of the recommendations and more explicit guidance in using the values for policy and other uses. Specific approaches need to be developed and tested for using available data to derive several reference points for intake of essential and other important food components that influence the risk of chronic disease. In addition, it would be critical to identify where data were insufficient for judgments to be made about the reference points and to make recommendations for research to fill these gaps. These reference points could provide a systematic way of organizing the scientific literature and identifying the strengths and weaknesses of existing data. In the judgment of the FNB, possible reference points (as illustrated in Figure 1) could be defined as follows:

• Deficient—Level of intake of a nutrient below which almost all healthy people can be expected, over time, to experience deficiency symptoms of a clinical, physical, or functional nature.

• Average Requirement—Mean level of intake of a nutrient or food component that appears, on the basis of experimental evidence, sufficient to maintain the desired biochemical/physiological function in a population. It is also important to know the variation in the mean requirement.

• Recommended Dietary Allowance—Level of intake of an essential nutrient or food component considered on the basis of available scientific knowledge, to be adequate to meet the known nutritional needs of practically all healthy persons. There will be a continuing need to redefine numerical recommendations. For some nutrients, other functional endpoints might be defined and included as criteria for the definition of recommended intakes.

• Upper Safe—Level of intake of a nutrient or food component that appears to be safe for most healthy people and beyond which there is concern that some people will experience symptoms of toxicity over time.

These multiple reference points would incorporate some aspects of the approach adopted by the Committee on Medical Aspects of Food Policy (COMA) of the United Kingdom in its 1991 report on Dietary Reference Values (DRVs) (COMA, 1991). The DRVs consist of three values. The first is the Estimated Average Requirement (EAR), which is the average requirement of a nutrient as shown in various study populations. The two other values are based on an assumption of normal distribution of nutrient requirements in

FIGURE 1 The concept of a safe intake range. The safe intake range is associated with a very low probability of either inadequacy or excess for an individual selected at random from the population. Adapted from Health and Welfare, Canada, 1983.

a population, with the understanding that information is usually inadequate to calculate the precise distribution of requirements. The Lower Reference Nutrient Intake is a value two standard deviations below the mean requirement and represents the lowest intake that will meet the needs of some individuals. In contrast, the Reference Nutrient Intake (RNI) is the value two standard deviations above the mean requirement. The RNI—which represents the amount of a nutrient sufficient or more than sufficient to meet the needs of most healthy people—is essentially equivalent in concept to the current RDAs of this country. In addition to DRVs for vitamins and minerals, the COMA report recommends intakes for several other dietary components —such as starches, sugars, fats, and fatty acids—where no precise requirement (or EAR) can be defined. The recommended intakes for these components are derived by a different process than that used for vitamins and essential minerals, one COMA describes as “pragmatic judgments” (p. 2) that represent intakes “consistent with good health, given the prevailing socio-cultural environment” (p. 13).

The FNB faces many challenges in developing its proposed approach. A future committee charged with this task and reviewing the literature would need to deal with suggestive, but incomplete, information on the potential for nutrients to reduce the risk of chronic disease and the amounts required to provide these effects; on the effective dose (analogous in concept to the average requirement); on the variability in the effective dose; on the chronic toxicity of large doses of nutrients; and on potential nutrient interactions. Of particular concern is the general lack of information on children, youths, and young adults. This information is required to develop recommendations that may affect longevity, health, and chronic disease. Most of the research to date on the reduction of risk of chronic disease is based on studies of middle-aged and older adults.

The FNB believes that future RDAs will need to have more flexibility to address multiple uses. The FNB recognizes that the present RDAs are not well suited for some applications (as shown in Table 1), for example, using RDAs for the nutritional labeling of foods requires that a single value for each nutrient be established as a standard. To meet the broad range of needs of users of the RDAs, the FNB proposes to develop a series of three publications.

One publication, an eleventh edition of the RDAs, would review what is known about essential nutrients and important food components with respect to the four proposed reference points: deficient, average requirement, recommended dietary allowance, and upper safe levels. In addition, a new

RDA committee would address, in the text of the report, issues of nutrient–nutrient interactions and the potential roles of nutrients and other food constituents in reducing chronic disease risk. The committee would review the literature in these areas for each nutrient or relevant constituent and give guidance on when and under what conditions it might be appropriate for certain individuals or population groups to strive for intakes that deviate from the RDAs.

A second publication would describe how the new RDAs could be used for the variety of purposes to which they are put. The traditional uses of the RDAs would be covered in this document. A third publication, intended for the public, would explain the principles and scientific evidence underlying the RDAs and present them in terms of dietary patterns for persons of specific age and physiologic states. It would also include recommended dietary patterns for population subgroups based on considerations of age, race, and ethnic dietary preferences. To contain costs, these three reports would be developed sequentially using a series of small committees overseen by a committee of FNB members.

The FNB would maintain this open process for developing future RDAs, by implementing new mechanisms to obtain wider participation. In addition to reviewing the literature, holding invitational workshops, and corresponding with experts, FNB members are considering new ways to obtain comments on the conceptual development of the RDAs and to evaluate the adequacy of the literature. Public meetings structured around the findings of the committee with respect to different controversial nutrients, symposia held in conjunction with professional society meetings, and research review monographs published for public comment will be planned to increase the involvement of the nutrition community.

With this concept paper, the FNB presents its initial ideas for a new approach to the RDAs. The FNB seeks constructive criticism, suggestions, and substantiated rebuttal so that our approach can be reviewed and modified. To advance this process, symposia are scheduled at nutrition-focused scientific meetings through 1994 to debate several of the outstanding issues discussed in this paper (see Appendix C for details). The FNB urges readers of this report to submit written remarks to the address below. Please include full literature citations and supporting documentation wherever appropriate.

The FNB looks forward to working with the interested nutrition community in determining the future of the RDAs.

Send comments to: RDA Comments, Food and Nutrition Board, Institute of Medicine/NAS, 2101 Constitution Avenue, N.W., Washington, D.C. 20418