Fat-free mass estimation by the two-electrode impedance method

In 202 healthy subjects (81 men, 121 women) aged 12-71 y, impedance (Z) was measured with a two-electrode analyzer. Fat-free mass was assessed by hydrodensitometry (FFMd). This population was randomized into two groups for cross-validation. In group 1 the relationship between ht2/Z at 1 MHz and FFMd was highly significant (r = 0.85, P less than 0.001). The equation for predicting FFMd from impedance, height2, weight, and age obtained in group 1 (r = 0.97) was applied to group 2 (r = 0.96) without reduction in r value. The accuracy of this equation was not different between men and women or between active and sedentary people. These data indicate that the two-electrode impedance method is a reliable and valid approach not only for the determination of extracellular water (as previously shown) but also for that of FFM.