Bioelectrical impedance analysis measurements as part of a national nutrition survey.

Since 1960 the National Center for Health Statistics has conducted seven national health examination surveys. All surveys included anthropometry. As the relations between various chronic diseases and body composition have been recognized, there has been considerable interest in assessing body composition in health examinations on the basis of nationally representative probability samples. I focus on considerations that influenced the decision to include bioelectrical impedance analysis (BIA) in a national nutrition survey. Tetrapolar, single-frequency (50 kHz) BIA was included in the third National Health and Nutrition Examination Survey (1988-1994) for persons aged > or = 12 y, resulting in > 17000 resistance and reactance measures in non-Hispanic white, non-Hispanic black, and Mexican American subjects. The usefulness of these data in producing national reference distributions for lean body mass and fat mass, however, is currently limited by the uncertain availability of generalizable, valid, reliable, cross-validated prediction equations for various age, sex, and racial-ethnic groups.