Evaluation of bioelectrical impedance analysis for body composition measurements in anorexia nervosa

Many established methods of measuring body composition are time consuming and require complex equipment which is not generally available. Bioelectrical impedance analysis is a technique which utilises the difference in conductivity between fat and lean tissues at radiofrequencies. It uses inexpensive equipment which is simple to use and does not involve the use of ionising radiation. We have evaluated this technique in 44 studies on 38 anorexic females with a wide range of body mass index. Fat free mass was obtained from the mean of three established methods. The initial calibration was derived from 21 studies on 19 anorexics. Fat free mass was regressed against impedance and body habitus parameters to establish the prediction equation with the smallest standard error (1.12 kg). Values of fat free mass derived using this prediction equation were then compared with the other methods in a prospective study. The error of the bioelectrical impedance technique compares favourably with the established methods, even in anorexic patients with very low body mass index.