Bioelectrical impedance analysis does not detect an increase in total body water following isotonic fluid consumption

Applied Physiology, Nutrition, and Metabolism, e-First Articles. Purpose: To determine if single-frequency foot-to-foot bioelectrical impedance analysis (BIA) can detect acute changes in total body water (TBW) following consumption of isotonic saline. All participants ate a sodium-free meal at 4 h prior to the data collection visit and had euhydration confirmed using urine specific gravity at the beginning of the experimental visit. Subjects drank 466 mL of isotonic saline (Na+ 140 mmol ·L−1) following baseline measures. Blood sampling and BIA were performed at baseline and every 30 min for 3 h after saline consumption. Ten healthy participants completed this study. Plasma volume (5%Δ, p< 0.001) and serum sodium concentration (1% Δ, p< 0.001) increased by 60 min and 90 min, respectively. Body mass (p< 0.001) displayed a biphasic response increasing to a peak at 30 min (+0.38 Δkg) and then decreasing to its minimum at 180 min (–0.35Δkg). BIA impedance (p = 0.678) was unaffected by the saline administration. BIA-derived TBW (p = 0.039) decreased from baseline starting at 150 min (0.21Δkg). Novelty Athletes and coaches wishing to achieve hyperhydration can do so thro ugh the consumption of isotonic fluid. 50 kHz foot-to-foot BIA-derived TBW is inadequate for measuring hyperhydration. Future studies should examine the physiological and performance effects of such a hyperhydration protocol.

Source: Applied Physiology, Nutrition, and Metabolism - April 17, 2019 Category: Physiology Authors: Evan L. Matthews Peter A. Hosick Source Type: research