A randomized trial modeling the effects of solutions with low to moderate glycerol and sodium concentrations on fluid balance in healthy, active adults.

Abstract

BACKGROUND: Ingestion of beverages with glycerol and electrolytes promotes fluid retention and fluid balance; however, more research is needed to determine the effects of low to moderate concentrations of these osmolytes. OBJECTIVES: To evaluate the impact of 0‒4.6% glycerol (GLY) and 0‒55 mM sodium (SOD) on fluid balance in healthy, active, euhydrated adults. METHODS: Thirty-seven participants (n = 22 male; n = 15 female; 30 ± 8 y; 75.5 ± 12.4 kg) consumed 28 oz of beverage followed by urine and body mass measurements for 210 min. In a double blind, randomly assigned, incomplete block, response surface design, each participant completed 3 trials, where they drank 1 of 6 beverages [0% GLY, 0 mM SOD (placebo); 0% GLY, 27.5 mM SOD; 0% GLY, 55 mM SOD; 2.3% GLY, 27.5 mM SOD; 4.6% GLY, 0 mM SOD; 4.6% GLY, 55 mM SOD]. A response surface regression model was fitted to predict the effects of GLY, SOD, and time on fluid balance (percentage change in body mass from baseline). Ninety-five percent confidence intervals were used to compare predicted mean outcomes. RESULTS: Glycerol (P < 0.001), SOD (P < 0.001), and time (P < 0.001) were significant terms in the model (adjusted r2 = 0.81). There were significant interactions for GLY by time (P = 0.001) and SOD by time (P < 0.001). At 210 min, fluid balance was predicted to be greater with ingestion of ≥1.5% GLY alone (‒0.55 ± 0.07% to ‒0.40 ± 0.06%) or ≥25 mM SOD alone (‒0.58 ± 0.05% to ‒0.21 ± 0.06%) compared with placebo (‒0.69 ± 0.06%), and with ingestion of ≥0.75% GLY plus ≥15 mM SOD (‒0.57 ± 0.04% to 0.05 ± 0.06%) compared with placebo (‒0.69 ± 0.06%). CONCLUSIONS: Relatively low concentrations of GLY by itself (≥1.5%) or in combination with electrolytes (≥0.75% GLY plus ≥15 mM SOD) promoted better fluid balance than placebo. These results help inform the minimum concentrations of GLY and/or SOD needed to promote fluid balance in healthy, active individuals; however, future research is needed to verify the model's predictions. This trial was registered at clinicaltrials.gov as NCT06185595.