Methodological considerations

摘要

In studies aimed at identifying protein and amino acid requirements a clear definition of objectives is important (Fereday et al. 1997; Millward et al. 1997). I define metabolic demands as what the organism needs, i.e. for maintenance plus additional needs for growth, pregnancy and lactation, efficiency of utilisation as the relationship between dietary intake and satisfaction of metabolic demands, and requirement as metabolic demands divided by efficiency of utilisation. We can measure requirement directly or calculate it after measuring metabolic demands and efficiency of utilisation. In terms of nutritional design, two types of studies are done. Experimental studies with proteins enable measurements of protein requirements and protein quality (Food and Agriculture Organization/World Health Organization/United Nations University, 1985; Millward et al. 1989) to be made, which in turn enable (at least to some extent) amino acid requirements to be identified if the limiting amino acid is known (Millward et al. 2000a). The advantage of such studies is that protein and amino acid requirement values are used mainly to formulate food-protein-based diets so that such studies are most relevant. Indeed, it is important to recognise that information about requirements already exists in terms of our understanding of what individuals eat, i.e. the relationship between growth, maintenance, body composition, morbidity and mortality, and intake. Thus, requirements can be defined as intakes which maintain function.