Estimation of body fat in Caucasian and African-American girls: total-body electrical conductivity methodology versus a four-component model

BACKGROUND: Obesity has been increasing dramatically in recent years among children, particularly African-American girls. Total-body electrical conductivity (TOBEC) is a simple way to measure body fat with minimal risk. OBJECTIVE: This study compared the agreement between the percentage of fat mass (%FM) predicted using two TOBEC equations with %FM measured by a four-component model in 73 Caucasian and 41 African-American girls. DESIGN AND MEASUREMENTS: %FM predicted using the TOBEC equations was compared with %FM from the four-component model based on measurements of body density, body water and bone mineral content. RESULTS: Analyses by linear regression analysis and by the Bland and Altman methods comparison procedure showed that the equation using the square root of the TOBEC zero-order Fourier coefficient and the subject's height yielded more accurate and more reproducible %FM, regardless of race, than the TOBEC linear equation, which was based on the zero-, first- and second-order Fourier coefficients. The Bland and Altman comparison further revealed that the accuracy and limits of agreement of the TOBEC linear equation were related to body fatness among the Caucasian girls. The relationship, however, disappeared when prepubescent girls and a girl with low %FM were excluded from the analysis. CONCLUSIONS: The TOBEC square root equation with adjustment for body geometry and length is recommended for use in adolescent girls, as it yielded better agreement with the criterion method. However, further validation of the TOBEC instrumentation for estimating body fat in prepubescent children and children with low body fat is warranted.