[Non-invasive measurement of body composition]

The concept of body composition covers the division of the body into a number of compartments. The most important are the fat mass (FM), the fat-free mass (FFM), the total body protein and the total body bone mineral content. Numerous methods for the measurement of body composition are available. The three classical methods for the measurement of FM and FFM, namely underwater weighing, measurement of total body potassium and measurement of total body water by isotope dilution, are often regarded as reference methods. However, newer methods such as computed tomography, neutron activation analysis and dual energy X-ray absorptiometry are increasingly used because of their reliability and ability for independent measurement of two or more components. Bioelectrical impedance analysis has become popular because of its clinical applicability. Three- or four-compartment models involving combination of two, three or more separate methods are more accurate than single methods, but are usually confined to research purposes because of the laborious measurement procedures. Computed tomography and dual energy X-ray absorptiometry have the unique possibility of regional measurements of body composition. Fat distribution and relative overweight may be estimated by simple anthropometric measures such as skinfold thicknesses. There are many applications for body composition measurements in research and clinical practice. These include treatment of obesity, growth hormone deficiency, diabetes mellitus and climacteric changes, as well as clinical nutrition and estimation of the hydration of dialysis patients and of critically ill intensive or surgical patients.