Carbohydrate Exerts a Mild Influence but Electrolytes are the Primary Driver of Fluid Retention Following Exercise-Induced Dehydration.

Abstract

Rapid and complete rehyration is important when athletes are competing multiple times in one day, recovering from illness, or restoring fluid balance following voluntary dehydration. Many studies have investigated the effects of graded concentrations of sodium and other electrolytes in rehydration solutions, however, no study to date has determined the effect of varying carbohydrate concentration on fluid retention when electrolyte concentrations are held constant. PURPOSE: To determine the effect of graded levels of carbohydrate on fluid retention. METHODS: Heat-acclimatized men (n=15) exercised in the heat for 90 minutes with no fluid to induce 2-3% dehydration. After a 30-min rest, they ingested one of five test beverages equal to 100% of body weight loss. This volume was administered every 10 min for 60 min in aliquots equal to 25, 25, 12.5, 12.5, 12.5, and 12.5% of body weight loss. The experimental beverages consisted of an artificially flavored placebo with no electrolytes (P), a similar placebo with electrolytes (P+E), 3%, 6%, and 12% carbohydrate solutions with electrolytes. All beverages contained the same type and concentration of electrolytes (18 mEq/L Na+, 3 mEq/L K+, 11 mEq/L Cl-). After rehydrating, subjects voided their bladders at 60, 90, 120, 180, and 240 min post-exercise and urine specific gravity and urine volume were measured. A final body weight was taken at 240 min to calculate percent fluid retained. RESULTS: Dehydration as percent of body weight lost did not differ between trials (2.64 ± 0.47%) and mean sweat loss and total fluid intake (2.05 ± 0.39 L and 2.05 ± 0.40, respectively) were also not different. Urine specific gravity was significantly higher for 6 and 12% carbohydrate at all time points following rehydration compared to P and P + E. Cumulative urine loss was significantly greater for P compared to all carbohydrate beverages. Fluid retention was significantly better for all carbohydrate beverages compared to P (66.3 ± 14.4%). P+E (71.8 ± 9.9%) was not different than water, 3% (75.4 ± 7.8%) or 6% (75.4 ± 16.4%) but was significantly less than 12% (82.4 ± 9.2%). CONCLUSION: Although carbohydrate exerted a mild influence on rehydration, electrolytes in the concentrations we tested were the primary driver for fluid retention and completeness of rehydration.