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

Background: Although the body mass index (BMI, kgm(-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.