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

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.