A new method (BIM) by bioelectrical impedance for the estimation of human whole body or local part fat volume is described. This method is based upon that the resistivity of adipose tissue is much greater than that of fat-free mass of which frequency characteristics shows β dispersion phenomenon. It is well known that the admittance locus of fat-free mass provides the semicircle. Because the impedance value of trunk is only 10 or 20% of the whole body impedance (Zall) between arm and leg used by the commercialized impedance fat meter, if the fat volume in the trunk increase, the estimation error in the fat volume estimated from Zall would increase. Therefore, instead of Zall, BIM adopts the impedances measured at 5 local parts which are antebrachium, brachium, trunk, femoral part and cruralis. We measured the impedance of each parts for the frequency range from 3kHz to 300kHz and calculate the admittance locus in order to obtain the conductance at much lower frequency (Ge) and much higher frequency (Ginf) than β dispersion frequency. Arms, trunk and legs are represented by parallel models which are cone shape and consists of fat layer and fat-free mass layer. And then we calculate the equivalent conductivity σ of parallel models from Ge or Ginf. From σ, fat volumes of local parts which are arm, trunk and leg and whole body are estimated. When we estimate the fat volume of trunk, in order to take into consideration the adipose tissue which distributes around organs in trunk like liver, stomach, and etc., the weighting function K which is statistically given is multiplied to the equivalent conductivity of trunk. The reference fat volume can be measured by hydrometry. We can conclude that (1) the impedance at the trunk must be measured to consider the fat volume in the trunk, (2) Ge or Ginf must be used instead of impedance at about 50kHz to estimate the fat volume, and (3) correlation coefficients between the whole fat volume measured by hydrometry and that by BIM with Ge and Ginf are about 0.77 and 0.94, respectively.
