Estimating Body Fatness from Bioelectrical Impedance Analysis and Skinfolds in Children

Abstract

Seventy-three children (mean age=6.5) were studied at the University of Vermont, Clinical Research Center. Percent body fat was determined for each child using three different methods, bioelectrical impedance analysis (BIA), dual energy x-ray absorptiometry (DEXA), and skinfolds. Impedance measurements were used to estimate fat free mass using the following equation: [(ht2/resistance)0.59+(wt × 0.065)+0.04]/[0.769–(0.0025 × age)–(0.019 × gender)]. Fat mass was then determined by subtracting the value of the fat free mass from total body weight and percent fat was calculated by dividing fat mass by body weight and multiplying by 100. Skinfold thicknesses were taken to determine body fatness using the Lohman equations. When the sum of the skinfolds was greater than 35mm, percent fat for boys was calculated as [(0.783 × sum SF)–1.7] and percent fat for girls was calculated as [(0.0546 × sum SF) + 9.7]. When the sum of skinfolds was less than 35mm, percent fat for boys was calculated as [(1.21 × sum SF)–[0.008(sum SF × sum SF)]–1.7] and percent fat for girls was calculated as [(1.33 × sum SF)–[0.013 × (sum SF × sum SF)] + 2.5]. DEXA values were determined using the pediatric software developed by the Lunar Radiation Corporation (Madison, WI). There was no statistical difference between percent body fat as measured by DEXA and skinfolds (DEXA=20.7,SF=19.9)(t=–1.3,p=.20). However, percent body fat as measured by BIA was significantly greater than that measured by DEXA (DEXA=20.7,BIA=22.1)(t=2.0,p=05). Body fatness from skinfolds was significantly correlated with DEXA (r=.77,p<.001). BIA was also significantly correlated with DEXA, but to a lesser degree than skinfolds (r=.66,p<.001). In our sample, skinfolds predicted body fatness more precisely than BIA. In a clinical setting, we recommend the use of skinfold calipers over BIA in determining percent body fatness in children.