ABSTRACT
All life is characterized by turnover and change. Nutrition is an integral part of this process and as a matter of course all living organisms take energy and nutrients from the environment. In humans this represents the normal dietary intake. The chemical reactions through which the dietary constituents exchange with constituents of the body are controlled to ensure that the metabolic function is maintained. As a general principle, the body adapts to conserve those components of limited availability in the environment. By and large, important mechanisms exist to ensure an adequate supply of protein, amino acids and nitrogen (Schoenheimer, 1942; Waterlow, 1968; Jackson, 1993). The chemical interchange is continuous, and ultimately the end-products pass out of the body as gases, solutes or solid material. The characterization of nutritional state is a formal expression of the extent to which diet has enabled normal function to be maintained. There are a number of different ways in which the nutritional state of an individual can be assessed and characterized. As our understanding develops the subtlety of the characterization increases in sophistication.
