Assessment of body composition in infants and children.

The aims of this review are to consider 1) the applications of pediatric body composition methodology; 2) criteria for determining choice of method; and 3) some future developments. The major applications are: development and validation of new methods; assessment of growth or nutritional status; public health applications, such as monitoring the increasing prevalence of pediatric obesity; interpretation of data on energy expenditure; and testing the functional significance of variation in body composition. An appreciation of the underlying theoretical models (two-component and multicomponent models) is essential to an understanding of the methodology, as is an appreciation of the fact that infants and children are not "chemically mature." The two-component model generates methods that, though limited by variation in the composition of fat-free mass, have accuracy that is acceptable so long as the method in question is chosen with care. Criteria for determining choice of method are provided. Multicomponent models have a more rigorous theoretical basis, but require access to techniques that are not universally available and not always practical for pediatric use. Bedside methods, notably bioelectrical impedance and skinfold thickness, can provide acceptable accuracy, but the precision of all methods limits their ability to measure changes in body composition.