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household in a manner likely to satisfy the needs of the individual household members.

This problem has been identified since at least 1970 when a Food and Agriculture Organization/World Health Organization (FAO/ WHO) report on requirements of iron demonstrated that simply computing the aggregate requirement of household members did not begin to address issues of estimating the amount of iron that needed to be supplied at the household level if adequacy of intake of the individual family members was to be expected. That is, when a diet providing the aggregate iron need is acquired and consumed by the household, it is likely that food (and iron) will be distributed in proportion to energy needs of the individuals. As a result, there will almost certainly be serious shortfalls in iron intake for women and very young children and surplus iron intakes for adult men and boys (FAO/WHO, 1970). Although the problem had been identified, practical approaches to resolution were much later in coming.

A possible solution to this problem—suggested but not developed in the 1970 report—is to estimate the required nutrient density of the household diet such that when that diet is shared in proportion to energy, there is high likelihood that the needs of all individuals would be met. By definition, such a diet provided in amounts to meet household energy needs would represent a nutritionally adequate household-level diet. The required household nutrient density is set with respect to the class of individuals with the highest nutrient density need. With the use of current FAO/WHO nutrient and energy requirement estimates and the exclusion of pregnant women from the consideration, it turns out that this is often pubescent boys and girls or women of childbearing age.

The calculation of required nutrient density is not as simple as computing the ratio of either the Estimated Average Requirement (EAR) or Recommended Dietary Allowance (RDA) for the nutrient to the average energy requirement. The calculations must take into account variability of the nutrient requirement, expected variability of the nutrient density in ingested diets, and assurance of adequacy for the targeted individual. The theoretical basis for such calculations was partially developed by the 1985 FAO/WHO/UNU committee and an operational approach was subsequently applied by Beaton. In an unpublished report to the Canadian International Development Agency in 1995, Beaton operationalized these concepts in developing guidelines for fortification of foods for refugees where the household was taken as the unit of observation (and of distribution). Because household-level calculations are most likely to be conducted in connection with planning rather than evalua-

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