AMDRs are expressed as percentages of total energy intake because their requirements, in a classical sense, are not independent of each other or of the total energy requirement of the individual. Each must be expressed in terms relative to the others. A key feature of each AMDR is that it has a lower and upper boundary, some of which are determined mainly by the lowest or highest value judged to have an expected impact on health. Above or below these boundaries, there is a potential for increasing the risk of chronic diseases.
Each type of DRI refers to the average daily nutrient intake of individuals over time. The amount consumed may vary substantially from day to day without ill effect in most cases. Moreover, unless otherwise stated, all values given for EARs, RDAs, AIs, and AMDRs represent the quantity of the nutrient or food component to be supplied by foods from diets similar to those consumed in the United States and Canada. Healthy subgroups of the population often have different requirements, so special attention has been given to the differences due to gender and age, and often separate reference intakes are estimated for specified subgroups.
For some nutrients (e.g., trace elements) a higher intake may be needed for healthy people if the degree of absorption of the nutrient is unusually low on a chronic basis (e.g., because of very high fiber intake). If the primary source of a nutrient is a supplement, a higher or lower percentage of the nutrient may be absorbed, so a smaller or greater intake may be required. In addition, an adverse effect may be demonstrated at a lower level of intake when the source of the nutrient is from a supplement rather than from a food. When issues such as these arise, they are discussed in each DRI report.
The DRIs apply to the apparently healthy population and while the RDAs and AIs are levels of intake recommended for individuals, meeting these levels would not necessarily be sufficient for individuals who are already malnourished. People with diseases that result in malabsorption syndrome or who are undergoing certain treatments, such as hemo- or peritoneal dialysis, may have increased requirements for some nutrients. Special guidance should be provided for those with greatly increased or decreased needs (e.g., decreased energy due to disability or decreased mobility). Although the RDA or AI may serve as the basis for such guidance, qualified health care personnel should make necessary adaptations for specific situations.