Historically, the goal has been to assess the apparent adequacy of total energy supply for a population or group of populations. An approach to the estimation of population energy needs was described in detail by James and Schofield (1990). Energy needs of each physiological stratum of the population—taking into account either actual or desirable body size and physical activity—are multiplied by the number of individuals in that stratum and these needs are aggregated for the population. Under the condition of overall adequacy judged against this estimate of aggregate need (which could be expressed as the total or per capita energy need), the assumption must be that, on a chronic basis, energy intake is distributed across strata and individuals in proportion to energy needs. If per capita supply meets or exceeds the per capita requirement (including allowance for wastage), then a satisfactory situation can and should exist. However, where total supply appears to fall short of total need, it must be accepted that the distribution of intakes is likely to be inequitable. Without information about that distribution, inferences cannot be drawn about the likely prevalence of inadequate intakes within the population. Interpretation is limited to the unit of observation —the population as a whole or sometimes a specific population subgroup for which food use data are available.
In theory, one could also assess per capita intake data for adequacy of other nutrients at the population level. The approach would have to involve a first step of generating a per capita requirement probably based on an intermediate nutrient density approach as discussed above for household intake data. It is not certain whether such an approach has ever been attempted. Approaches based on a per capita recommended intake (e.g., demographically weighted Recommended Dietary Allowances [RDAs]) will not work for the same reasons discussed for household-level intake data. That is, it is unreasonable to assume equitable (proportional to actual need) distribution of nutrients. Methodologies for population-level assessment of nutrient supply are in their infancy and any attempt at such assessment should be scrutinized with great care. In the past the most commonly used approach was the simple comparison of per capita supply with the RDA, with or without even demographic weighting. That is an inappropriate use of the RDAs, past or present (Beaton, 1999).