Accuracy of bioelectrical impedance spectroscopy in measuring changes in body composition during severe weight loss

BACKGROUND: Bioelectrical impedance spectroscopy (BIS) is an attractive method for measuring body composition because it is noninvasive, simple, and cheap. The effect of obesity on the accuracy of impedance measurements has been recognized for some time, but no conclusive explanations or ways to correct the measurement errors have been published. We studied the effect of the composition of weight loss on the accuracy of BIS to measure changes in body fluid volumes during severe weight loss. Within subjects the effect of variable losses of fat mass was studied. METHODS: In 10 morbidly obese female subjects who underwent gastric reduction surgery, changes in total body water (TBW) and extracellular water (ECW) were monitored for 1 year by deuterium (Deu) and bromide (Br) dilution and by BIS. Measurements were performed before the operation and after 2 weeks, 3 months, and 1 year. Extrapolated resistance values of extracellular (Recw) and intracellular water (Ricw) were used in mixture equations for calculat...