BIOELECTRICAL-IMPEDANCE AND BODY-COMPOSITION - PRESENT STATUS AND FUTURE-DIRECTIONS

Single-frequency bioelectrical impedance analyzers used to assess body composition are being replaced by multiple-frequency analyzers. At lo w frequencies, the current flows primarily through extracellular fluid s; at high frequencies, it completely penetrates all body tissues. Mea sures of bioelectrical impedance at multiple frequencies can different iate total and extracellular fluid compartments in the body. This has considerable value for assessing clinical and nutritional status. Impe dance measures at a single frequency contain only a small window of th e available impedance spectrum information, which may explain the diff iculty in discriminating among individuals. The impedance spectrum and its analysis may provide a much clearer picture of individual differe nces in body water and body composition. With increasing clinical uses of bioelectrical impedance in individuals and sample populations, the use of multiple-frequency impedance may help to elucidate differences that are not discernible with single-frequency impedance.