Prediction of body fat in 12-y-old African American and white children: evaluation of methods

Background: The prevalence of obesity is increasing in children. Validation of methods of predicting fatness in African American and white children could help to identify children at high risk. Objective: We assessed published methods for determining body fat in 12-y-old male and female white and African American schoolchildren. Design: The body fat of 114 children was measured with the use of dual-energy X-ray absorptiometry, underwater weighing (densitometry), measurement of skinfold thicknesses, isotope dilution ((H2O)-O-18), and bioelectrical impedance analysis. Formulas derived from these data and from published reports were compared by using the Bland-Altman approach. Results: Calculation of percentage of body fat by using an equation predicting body fat in kg and dividing by the current weight was the criterion method against which the other methods were compared. Four-compartment models had the smallest variability across the range of body fat, and 2 of these models differed from the criterion method by 1-2%. Six methods (the Pennington 4-compartment model, the Wells et al 4-compartment model, the isotope dilution model, dual-energy X-ray absorptiometry, the Pennington skinfold thickness model, and the Pennington density model) provided specificity > 90%, an estimate of body fat that was within the 95% CI of the criterion method, and a difference from the criterion method that was < 2%. Bioelectrical impedance analysis was the least acceptable method. Conclusions: A 4-compartment model in which body fat in kg is divided by current body weight and multiplied by 100 provides the best estimate of percentage of body fat. The isotope dilution and body density models provide estimates within 2% of the estimate provided by the 4-compartment model. Other models do less well.