Estimation of percentage body fat in 6-to 13-year-old children by skinfold thickness, body mass index and waist circumference

We evaluated the accuracy of skinfold thicknesses, BMI and waist circumference for the prediction of percentage body fat (PBF) in a representative sample of 372 Swiss children aged 6-13 years. PBF was measured using dual-energy X-ray absorptiometry. On the basis of a preliminary bootstrap selection of predictors, seven regression models were evaluated. All models included sex, age and pubertal stage plus one of the following predictors: (1) log-transformed triceps skinfold (logTSF); (2) logTSF and waist circumference; (3) log-transformed sum of triceps and subscapular skinfolds (logSF2); (4) log-transformed sum of triceps, biceps, subscapular and supra-iliac skinfolds (logSF4); (5) BMI; (6) waist circumference; (7) BMI and waist circumference. The adjusted determination coefficient (R-adj(2)) and the root mean squared error (RMSE; kg) were calculated for each model. LogSF4 (R-adj(2) 0.85; RMSE 2.35) and logSF2 (R-adj(2) 0.82; RMSE 2.54) were similarly accurate at predicting PBF and superior to logTSF (R-adj(2) 0.75; RMSE 3.02), logTSF combined with waist circumference (R-adj(2) 0.78; RMSE 2.85), BMI (R-adj(2) 0.62; RMSE 3.73), waist circumference (R-adj(2) 0.58; RMSE 3.89), and BMI combined with waist circumference (R-adj(2) 0.63; RMSE 3.66) (P<0.001 for all values of R-adj(2)). The finding that logSF4 was only modestly superior to logSF2 and that logTSF was better than BMI and waist circumference at predicting PBF has important implications for paediatric epidemiological studies aimed at disentangling the effect of body fat on health outcomes.