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

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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%∆, p < 0.001) and serum sodium concentration (1%∆, 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∆kg) and then decreasing to its minimum at 180 min (–0.35∆kg). BIA impedance (p = 0.678) was unaffected by the saline administration. BIA-derived TBW (p = 0.039) decreased from baseline starting at 150 min (0.21∆kg). Novelty • Athletes and coaches wishing to achieve hyperhydration can do so through 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.

Original languageEnglish
Pages (from-to)1116-1120
Number of pages5
JournalApplied Physiology, Nutrition and Metabolism
Issue number10
StatePublished - 2019


  • Athlete performance
  • Body composition
  • Exercise nutrition
  • Hydration
  • Physiology
  • Sports nutrition


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