Validating Technology with Bioelectrical Impedance Analysis
Bioelectrical impedance analysis (BIA) is a widely used method for estimating the human body composition. The technology is relatively simple, quick and noninvasive. BIA is currently used in diverse settings, including the U.S. Military, health practitioner offices, health clubs, and hospitals, and across a spectrum of ages, body weights, and disease states. Despite a general public perception that BIA is merely a measurement of “body fat”, the technology actually determines the electrical impedance of body tissues, which provides an estimate of total body water (TBW). Using values of TBW derived from BIA, one can then estimate fat-free mass (FFM) and body fat. In addition to its use in estimating body fat, BIA is beginning to be used in the estimation of body cell mass and TBW in a variety of clinical conditions.
BIA measures the opposition of body tissues to the flow of a small alternating current. Impedance is a function of two components: the resistance of the tissues themselves, and the additional opposition (reactance) due to the capacitance (cell charge energy) of cellular membranes.
Application of BIA increasingly use multi-frequency measurements, or a frequency spectrum, to evaluate differences in body composition caused by individual subject’s clinical and nutritional status (e.g., “phase angle” or ratio between “reactance” and “resistance”, ratio between moisture inside the cells, or “intracellular water” (ICW), and moisture outside the cells, or “extracellular water” (ECW), and “parallel capacitance” or ion concentration gradient essential for cell survival.