Does Body Mass Index Accurately Reflect Body Fat? A Comparison of Anthropometric Measures in the Longitudinal Assessment of Fat Mass

Abstract

Objective To determine which anthropometric measure best correlates with change in fat mass (FM) over time. Methods The authors performed a retrospective cohort study of 76 obese patients (mean body mass index [BMI] 38 kg/m2 and mean age 13 years) presenting to an obesity clinic between 2005 and 2010. For each patient, during 2 visits, FM was measured by bioelectrical impedance analysis and the following measures obtained: BMI, waist circumference, hip circumference, and neck circumference. Correlation coefficients and linear regression analyses were calculated to examine the relationship between each measure and FM. Results Change in BMI correlated better with change in FM than any other measure and had the strongest effect on change in FM ( P < .01, R2 = .887). The best regression model included BMI only ( R2 = .891); without BMI, the model was significantly worse ( R2 = .521). Discussion In the clinical management of obese children, BMI is an adequate measure of change in FM.