The prediction of body fatness by BMI and skinfold thicknesses among children and adolescents

BACKGROUND: Although the body mass index (BMI, kg m(-2)) is widely used as a measure of adiposity, it is a measure of excess weight, rather than excess body fat. It has been suggested that skinfold thicknesses be measured among overweight children to confirm the presence of excess adiposity. OBJECTIVE: The present study examined the additional information provided by skinfold thicknesses on body fatness, beyond that conveyed by BMI-for-age, among healthy 5- to 18-years old (n = 1196). METHODS AND PROCEDURES: Total body dual-energy X-ray absorptiometry (DXA) provided estimates of % body fat, and the sum of two skinfolds (triceps and subscapular) was used as an indicator of the overall skinfold thickness. RESULTS: As assessed by the multiple R(2)s and the residuals of various regression models, information on the skinfold sum significantly ( p < 0.001) improved the prediction of body fatness beyond that obtained with BMI-for-age. For example, the use of the skinfold sum, in addition to BMI-for-age, increased the multiple R(2)s for predicting % body fat from 0.81 to 0.90 (boys), and from 0.82 to 0.89 (girls). The use of the skinfold sum also reduced the overall prediction errors (absolute value of the residuals) for % body fat by 20-30%, but these reductions varied substantially by BMI-for-age. Among overweight children, defined by a BMI-for-age >/=95th percentile, the skinfold sum reduced the predication errors for % body fat by only 7-9%. CONCLUSIONS: Although skinfold thicknesses, when used in addition to BMI-for-age, can substantially improve the estimation of body fatness, the improvement among overweight children is small.