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

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.

Thirty-eight overweight adults (BMI, 25.0 to 29.9 kg/m2; age, 18 to 44 years; 31 women) participated in a 6-month, randomized, double-blind, 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 (%FM(T-Man)) and by Jebb et al. (%FM(T-Jebb))] and the 4C model (%FM(4C)).

Subjects in the experimental group lost 0.9%FM(4C) (p = 0.03), a loss that did not reach significance using leg-to-leg BIA (0.6%FM(T-Man), p = 0.151; 0.6%FM(T-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.

Leg-to-leg BIA performed reasonably well in predicting decreases in %FM in this group of overweight adults but resulted in wide SDs vs. %FM(4C) in individuals. Cross-sectional determinations of %FM of overweight individuals using leg-to-leg BIA should be interpreted with caution.