Nutritional assessment

Measurements of body composition are made to assess nutritional status. The measurements used for these studies should be selected on the basis of reliability, as well as simplicity and costs, and reliability depends on the information required. In normal adults simple estimates of fat and lean tissue (LBM), i.e. the anthropometric measurements of weight, height and skin fold thickness, should be sufficient since the proportions, in LBM, of water, protein and bone mineral are relatively constant. Measurements of body water (by isotope dilution or bioelectrical impedance) allow indirect estimates of fat and LBM that are reliable, provided that water is a constant proportion of LBM. In disease states, however, including renal disease, it is well established that the proportion of water in LBM varies from significant water overload to dehydration. In disease, it is important to determine not only total LBM but also the quality of LBM, determining essential body protein as well as body water. Body protein can be measured directly by nuclear techniques. This procedure should be more readily available for the clinical investigation of nutritional status.