greater conservation of many nutrients. Moreover, nutrients may undergo net losses due to physiological mechanisms regardless of the nutrient intake. Thus, for some nutrients there may not be a basis for EAR values that are different from those for nonpregnant or nonlactating women of comparable age.
Reference heights and weights are useful when more specificity about body size and nutrient requirements are needed than that provided by life stage categories. For example, while the EAR may be developed for the 4- to 8-year-old age group, a small 4-year-old child may be assumed to require less than the EAR for that age group, whereas a large 8-year-old child may require more than the EAR. Based on the model for establishing RDAs however, the RDA (and for that matter, an AI) should meet the needs of both.
In cases where data regarding nutrient requirements are reported on a body-weight basis, it is necessary to have reference heights and weights to transform the data for comparison purposes. Frequently, where data regarding adult requirements represent the only available data (e.g., on adverse effects of chronic high intakes for establishing ULs), extrapolating on the basis of body weight or size becomes a possible option to estimate ULs for other age groups. Thus when data are not available, the EAR or UL for children or pregnant women may be established by extrapolation from adult values on the basis of body weight.
The most up-to-date data providing heights and weights of individuals in the United States and Canada when the DRI process was initiated in 1995 were limited to anthropometric data from the 1988–1994 Third National Health and Nutrition Examination Survey (NHANES III) in the United States and older data from Canada. Reference values derived from the NHANES III data and used in early DRI reports are given in Table 4-1.
These earlier values were obtained as follows: the median heights for the life stage and gender groups through age 30 years were identified, and the median weights for these heights were based on reported median body mass indexes (BMIs) for the same individuals. Since there is no evidence that weight should change as adults age