Differences in estimates of percent body fat using bioelectrical impedance

The purpose of the present investigation was to analyze the replicability of percent body fat (% fat) determined from Bioelectrical Impedance Analyses (BIA) after 2 different postprandial time periods and by 2 different technicians. The BIA % fat measures were also compared to those determined from skinfold measurements (SF) and hydrostatic weighing (HW). Fifteen physically active men had body composition determined on 4 separate days over a 2 week period under controlled conditions, once each week after fasting for 12 hours and once after 3 hours. Each day the subjects had BIA and SF measures taken by different trained technicians. Once each week the subjects also were hydrostatically weighed (HW). There were no differences for either BIA or SF between the 2 postprandial time periods. There were significant differences between technicians for both BIA and SF (p < 0.01), although the relationships between technicians were good (r = 0.90 and 0.95, respectively). Mean values for BIA (11.8 +/- 3.2%) and HW (11.0 +/- 7.2%) were similar, however, the correlation was only r = 0.50. These results indicate that although BIA gave relatively consistent values, it regressed both low and high % fat values towards the mean of the sample.