Kamijo et al examined whether carbohydrates in beverages could promote enhanced fluid retention after heat and exercise-induced dehydration, and if this improvement was a result of an enhanced renal sodium reabsorption rate due to insulin secretion. Seven healthy young men participated in high carbohydrate, low carbohydrate, and no carbohydrate rehydration trials during which they drank beverages with varying concentrations of fructose and glucose after exercising in a hot environment. Each participant drank the same amount of liquids as they lost in total body weight within 30 minutes of exercising. Plasma volume, plasma glucose, serum insulin, plasma sodium concentrations, and renal clearances were measured at predetermined intervals for 60 minutes before and 180 minutes after the beverages were consumed. Each trial was conducted at least seven days after the previous trial to avoid any potential prolonged effects. Researchers found that consuming high carbohydrate beverages led to lower sodium excretion in the urine, higher fluid and sodium retentions, and faster plasma volume recovery after heat and exercise-induced dehydration. The authors concluded that “Carbohydrate in beverages enhances renal Na+ reabsorption, and insulin is possibly involved in this enhancement.”
The strengths of this study included the interval monitoring of plasma glucose levels, serum insulin, plasma sodium concentrations, and renal clearances and the spacing of rehydration trials to avoid potential prolonged effects on subsequent trials. A limitation of this study is the small sample size of seven males which limits the generalizability of the findings.
Study Abstract: http://www.ncbi.nlm.nih.gov/pubmed/22874424