Time-course changes in fluid balance following ingestion of a novel glycerol-electrolyte solution in a randomized trial

This randomized trial tested the effects of a novel glycerol-electrolyte solution (GES) compared with placebo on fluid balance for 8 h. Twenty-five (12 female, 13 male) healthy, active adults (30 ± 7 y, 76.91 ± 13.27 kg) completed two trials in a randomized, counterbalanced order. After arriving at the laboratory euhydrated, participants emptied their bladder, then had baseline body mass measured. Participants consumed 1 L of GES (0.75% glycerol, 40 mmol/L sodium, 15 mmol/L potassium, 8 mmol/L magnesium, 5 mg calcium) or placebo (water with flavor and sweetness matched to GES) followed by urine collection and body mass measurements for 8 h. A two-way repeated-measures ANOVA (beverage × time) was conducted, followed by Tukey's HSD test. Values are difference between beverages ± 95% CI. There was a significant effect of beverage, with fluid balance higher (0.15 ± 0.03%, p < 0.001) and urine output lower (-112 ± 23 g, p < 0.001) in the GES versus placebo trials across the 8-h observation period. There was also a beverage-by-time interaction effect: fluid balance was higher and urine output was lower 2 h (0.23 ± 0.14% and - 159 ± 98 g, p < 0.001), 3 h (0.19 ± 0.15% and - 144 ± 110 g, p = 0.001), and 4 h (0.18 ± 0.15% and - 137 ± 117 g, p < 0.01) with GES versus placebo. In summary, GES supported greater net fluid balance than placebo. The strongest pairwise differences occurred at 2-4 h, while the overall beverage effect was present across the full 8 h.