Effect of acute changes in hydration on body composition estimates from bioimpedance analysis

Abstract

Bioimpedance spectroscopy (BIS) has been shown to provide accurate estimates of acute changes in hydration. This study examined the effects of acute hydration changes on estimates of fat-free mass (FFM) and fat mass (FM) measured by BIS and single frequency bioimpedance analysis (SF-BIA) as compared to dual energy x-ray absorptiometry (DXA) in 17 young adults (15 F, 2 M). A 4-day dehydration/rehydration protocol and two SF-BIA instruments were used in this study. Although all bioimpedance methods provided estimates of FFM comparable to DXA estimates at baseline and after dehydration, BIS estimates were the most highly correlated (r2 = 0.950 at both time points) and the least variable (SEE = 1.99 kg and 2.03 kg, respectively). After rehydration, greater variability and lower correlations with DXA were observed for all three bioimpedance estimates with SEE ranging from 3.18 kg to 9.71 kg. Correlations ranged from 0.800 to 0.850 for the SF-BIA instruments; however, the correlation between BIS-FFM and DXA-FFM estimates declined sharply (r2 = 0.472). Estimates of FM were comparable among methods at all time points, and all estimates were highly correlated (r2 = 0.94–0.99) with DXA-FM. BIS appears to perform better than SF-BIA for measuring FFM at baseline and in a dehydrated state in healthy, young, non-obese subjects. Rehydration appears to affect the accuracy of BIS and SF-BIA FFM estimates. In contrast, all methods provided comparable estimates of FM regardless of hydration status. Support: USDA Hatch ARZT-136529-H-23-128.