## Reference Values Which to Use and When

As mentioned previously, there are two main uses of reference values: to assess diets for adequacy or excess and to plan diets (Figure 1). Although these may seem to be the same, in many ways the best reference values to use in these situations may be quite different from each other on a quantitative basis. In addition, each of these major functions is frequently applied in two different situations: to a group's intake (i.e., the intake of a population or subpopulation) or to an individual's intake.

Using DRIs to plan diets If the goal is to plan a diet or menu for a specific group so that the nutrient intake of all but a small number (e.g., 2 or 3%) in the group will have their needs met, it is not necessary for each person to consume at least the RDA; this actually overstates the need of almost all individuals. It is only necessary that the nutrient be consumed such that the intake of only 2 or 3% would be below the EAR. Thus, the goal would be to have a very low percentage of intakes below the EAR (Figure 4).

On the other hand, if one is planning a diet for the individual, and there is little knowledge about the individual other than his or her gender and age, then one would want to provide what is thought to be adequate for almost everyone in the group, which is the RDA—by definition set at 2 SD above the median or average requirement (EAR)—or the AI.

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Usual intake of nutrient (amount /day)

Figure 6 Example of assuming that when the mean intake of a population group is equal to the RDA, there will be a low prevalence of inadequacy. As shown, there may still be a substantial proportion of the population with intakes below the EAR, which would be a better estimate of the prevalence of inadequacy.

Whether this occurred or not would depend on whether the RDA was based on the mean intake of a population in which no one was inadequate or whether the RDA came from data for which some members of the population had inadequate intakes and thus demonstrated one or more possible criteria of inadequacy, which are usually not possible to determine. By using the EAR as the cutoff to determine the prevalence of inadequacy (this applies to those nutrients for which requirements are symmetrically or normally distributed), it is possible to set an acceptable level of inadequacy in situations of scarce resources in which it is not possible to assume that all have an adequate intake.

Using DRIs to assess diets Frequently, such as when considering whether to fortify the food supply with a specific nutrient or when evaluating the nutritional status of a subgroup in the population, it is necessary to assess the diets of groups through surveys of food intake and from such surveys determine which nutrients may be consumed at inadequate levels. If data on intakes for the group of interest are available, and the group possesses similar characteristics to the individuals studied when deriving the EARs, it is possible to estimate the prevalence of inadequacy in the group of interest from their intake data without information on their requirements or variation in intake.

This is a key reason for establishing EARs for nutrients, and it replaces the questionable past practice of comparing intakes to the RDA. Frequently when this was done, a group might appear to be at low risk of inadequacy because the mean intake of the group as a whole for a nutrient might be at or above the RDA, despite a sizable portion of the group being below their individual requirements, if they had been determined (Figure 6).

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