Bioelectrical impedance vs. four-compartment model to assess body fat change in overweight adults

Objective: The Tanita TBF-305 body fat analyzer is marketed for home and clinical use and is based on the principles of leg-to-leg bioelectrical impedance analysis (BIA). Few studies have investigated the ability of leg-to-leg BIA to detect change in percentage fat mass (%FM) over time. Our objective was to determine the ability of leg-to-leg BIA vs. the four-compartment (4C) model to detect small changes in %FM in overweight adults. Research Methods and Procedures: Thirty-eight overweight adults (BMI, 25.0 to 29.9 kg/m(2); age, 18 to 44 years; 31 women) participated in a 6-month, randomized, doubleblind, placebo-controlled study of a nutritional supplement. Body composition was measured at 0 and 6 months using the Tanita TBF-305 body fat analyzer [using equations derived by the manufacturer (%FMT-Man) and by Jebb et al. (%FMT-Jebb)] and the 4C model (%FM4C). Results: Subjects in the experimental group lost 0.9%FM4C (p = 0.03), a loss that did not reach significance using leg-to-leg BIA (0.6%FMT-Man, P = 0.151; 0.6%FMT-Jebb, p = 0.144). We observed large standard deviations (SDs) in the mean difference in %FM between the 4C model and the Tanita(Manufacturer) (2.5%) and Tanita(Jebb) (2.2%). Ten subjects fell outside +/- 1 SD of the mean differences at 0 and 6 months; those individuals were younger and shorter than those within +/- 1 SD. Discussion: Leg-to-leg BIA performed reasonably well in predicting decreases in %FM in this group of overweight adults but resulted in wide SDs vs. %FM4C in individuals. Cross-sectional determinations of %FM of overweight individuals using leg-to-leg BIA should be interpreted with caution.