Fat mass index performs best in monitoring management of obesity in prepubertal children.

OBJECTIVE An early and accurate recognition of success in treating obesity may increase the compliance of obese children and their families to intervention programs. This observational, prospective study aimed to evaluate the ability and the time to detect a significant reduction of adiposity estimated by body mass index (BMI), percentage of fat mass (%FM), and fat mass index (FMI) during weight management in prepubertal obese children. METHODS In a cohort of 60 prepubertal obese children aged 3-9 years included in an outpatient weight management program, BMI, %FM, and FMI were monitored monthly; the last two measurements were assessed using air displacement plethysmography. The outcome measures were the reduction of >5% of each indicator and the time to achieve it. RESULTS The rate of detection of the outcome was 33.3% (95% CI: 25.9-41.6) using BMI, significantly lower (p<0.001) than either 63.3% using %FM (95% CI: 50.6-74.8) or 70.0% (95% CI: 57.5-80.1) using FMI. The median time to detect the outcome was 71 days using FMI, shorter than 88 days using %FM, and similar to 70 days using BMI. The agreement between the outcome detected by FMI and by %FM was high (kappa 0.701), but very low between the success detected by BMI and either FMI (kappa 0.231) or %FM (kappa 0.125). CONCLUSIONS FMI achieved the best combination of ability and swiftness to identify reduction of adiposity during monitoring of weight management in prepubertal obese children.