menstruating women) the requirement distribution is known to be skewed rather than normal. For nutrients with skewed requirement distributions, the approach to assess individual intakes proposed in this chapter is not appropriate.
The larger the CV (and thus the standard deviation), the larger the range of possible values for an individual's requirement for that nutrient, and the greater the uncertainty about what the individual's requirement for that nutrient might be. Even in the hypothetical case in which the individual's usual nutrient intake is known, uncertainty remains about whether the usual intake is adequate, because that individual 's requirement is not known.
Recommended Dietary Allowances (RDAs) have been established as a target or goal for intake by an individual, and it can be assumed that individuals whose usual intakes are above the RDA are likely to be meeting their individual requirements and thus have adequate intakes. However, the converse is not true. For this reason the RDA is not a useful reference standard for assessing an individual's intake. Intakes below the RDA cannot be assumed to indicate that an individual's intake is inadequate. The RDA, by definition, exceeds the actual requirements of all but 2 to 3 percent of the population, so many of those with usual intakes below the RDA may be meeting their individual requirements. The likelihood of nutrient inadequacy, however, increases as the usual intake falls further below the RDA.
As discussed in the previous section, however, usual intakes are unobservable in practice. Thus, one is limited to comparing the observed mean intake to the DRIs in order to assess adequacy. Subsequently in this chapter it will be demonstrated that due to the typically high day-to-day variability in intakes for most nutrients, one may not be able to conclude that an individual's usual intake is adequate even if the observed mean intake is larger than the RDA. Thus, comparing an individual's observed mean intake to the RDA is not recommended as a means for determining nutrient adequacy for the individual.
If an Adequate Intake (AI) rather than an EAR was set for a nutrient (e.g., calcium, vitamin D), it may be used in a more limited way as described in the next section.
The third step in individual assessment is to assess the data to answer the question, On the basis of an individual's observed intake over a small number of days, is that individual's usual intake of the nutrient adequate and at low risk of adverse effects?