Aim: The aim of this study was to evaluate the validity of foot-to-foot bioelectrical impedance analysis (FF-BIA) in the measurement of body composition in overweight and obese children and their parents by comparison to dual-energy X-ray absorptiometry (DXA).
Methods: Seventeen, 7-12 year old overweight and obese children (6 boys, 11 girls) and 17 parents (5 fathers, 12 mothers) were evaluated for body composition with FF-BIA and DXA. Measures of percent body fat (PBF), fat mass (FM) and fat free mass (FFM) derived from FF-BIA and DXA were compared. Measures of validity were determined by Pearson correlations between FF-BIA and DXA, paired t-tests to assess mean differences, as well as biases and limits of agreement using the Bland Altman tests.
Results: FF-BIA produced estimates of body composition that were highly correlated with DXA in overweight and obese children and parents. For children, the correlations for PBF, FM, and FFM were 0.85, 0.97, and 0.94, respectively. For parents, the correlations for PBF, FM, and FFM were 0.92, 0.97, and 0.91, respectively. However, mean differences between FF-BIA and DXA were significant in children but not in parents. Bland-Altman tests of agreement showed moderate to large within-subject differences in body composition variables between FF-BIA and DXA.
Conclusions: FF-BIA is strongly related to DXA in the measurement of body composition in both overweight and obese preadolescent children and parents, but the two measures may not be used interchangeably. Although FF-BIA may lack the precision to assess small changes in body composition in overweight and obese individuals, it is appropriate for epidemiological use.