The reasoning used is described for each nutrient in Chapters 4 through 12.

The development of DRIs expands on the periodic reports called Recommended Dietary Allowances, which have been published since 1941 by the National Academy of Sciences. The chart on the inside back cover gives the recommended intake levels, whether RDAs or AIs, for the B vitamins and choline by life stage and gender group. Uses of DRIs appear in Box S-2. The transition from using RDAs alone to using all the DRIs appropriately will require time and effort by health professionals and others.

The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirement of nearly all (97 to 98 percent) healthy individuals in a particular life stage (life stage considers age and, when applicable, pregnancy or lactation) and gender group.

The process for setting the RDA depends on being able to set an Estimated Average Requirement (EAR). That is, the RDA is derived from the nutrient requirement; therefore, if an EAR cannot be set, no RDA will be set. The EAR is the daily intake value of a nutrient that is estimated to meet the nutrient requirement of half the healthy individuals in a life stage and gender group. Before setting the EAR, a specific criterion of adequacy is selected based on a careful review of the literature. When selecting the criterion, contemporary concepts of the reduction of disease risk are considered along with many other health parameters.

If the standard deviation (SD) of the EAR is available and the requirement for the nutrient is normally distributed, the RDA is set at 2 SDs above the EAR:

If data about variability in requirements are insufficient to calculate an SD, a coefficient of variation for the EAR of 10 percent is ordinarily assumed in this report.

The resulting equation for the RDA is then