Characteristics of body water distribution in healthy adults measured by multi-frequency bioelectrical impedance analysis

Objective: To investigate the characteristics of the ratio of extracellular water (ECW) to total body water (TBW) volume (ECW/TBW) in a large group of healthy adults, measured by multi-frequency bioelectrical impedance (bioimpedance) analysis (MF-BIA). Subjects and methods: The correlation between ECW and TBW was studied in 957 healthy adults who underwent general medical examinations. Differences between measured and predicted ECW from ECW–TBW correlation equations (ΔECW) were calculated, and possible factors for non-zero ΔECW were explored. To investigate the influence of percent fat mass (%FM) on ECW/TBW, the ECW/TBW values of “lean” and “obese” groups, classified by %FM, were compared. ECW/TBW was also compared between “non-obese” and “obese class I-II” groups, classified by the body mass index for both genders. Results: ECW and TBW showed strong positive correlations in both genders. ΔECW was within ±0.2 L and increased with advancing age; ECW/ TBW also increased. There were no significant differences in ECW/TBW between the “lean” and “obese” groups in either gender, or between the “non-obese” and “obese class I-II” groups in the female group. Conclusions: ECW/TBW measured by MF-BIA was considered to be an index of body water distribution in healthy adults ranging from “lean” to “obese class I-II,” which is not significantly affected by body fat.