Does adipose tissue influence bioelectric impedance in obese men and women?

Bioelectric-impedance analysis overestimates fat-free mass in obese people. No clear hypotheses have been presented or tested that explain this effect. This study tested the hypothesis that adipose tissue affects measurements of resistance by using data for whole body and body segment resistance and by using muscle, adipose tissue, and bone volumes from magnetic resonance imaging for 86 overweight and obese men and women (body mass index >27 kg/m(2); age 38.5 +/- 10.2 yr). In multiple-regression analysis, muscle volumes had strong associations with resistance, confirming that the electric currents are conducted primarily in the lean soft tissues. Subcutaneous adipose tissue had a slight but statistically significant effect in women, primarily for the leg, suggesting that adipose tissue can affect measured resistance when the volume of adipose tissue is greater than muscle volume, as may occur in obese women in particular. This resulted in a slight overestimation of fat-free mass (e.g., +3 kg) when a bioelectric-impedance-analysis equation calibrated for nonobese female subjects was applied.