According to the study by Erin L. McCleave, and colleagues of The University of Texas at Austin, the endurance gain likely reflects the added protein as well as a mix of carbohydrates, compared to a standard "single-carb" drink.
Studies have shown that carbohydrate-containing beverages increase endurance exercise performance, compared to water and placebo drinks. Some previous studies have suggested that adding a moderate amount of protein to a low- or moderate-carbohydrate supplement can further enhance endurance.
In their effort to develop a more effective supplement, the researchers switched from a single source of carbohydrate (dextrose) to a combination of three carbohydrates: glucose, fructose, and maltodextrin.
"Multiple sources of carbohydrate appear to increase exogenous carbohydrate oxidation," said the authors.
The new formulation improves exercise endurance in female athletes, compared to a standard dextrose-only supplement. The protein plus mixed-carb (and low-carb) supplement "improved performance despite containing 50 percent lower carbohydrate content and approximately 30 percent fewer calories," said McCleave and co-authors.
"This may be an important consideration for those individuals concerned about body weight and caloric intake," they added.
The study has been published in The Journal of Strength and Conditioning Research.