A "low-carb, mixed-carb" sports drink with added protein leads to prolonged endurance performance in trained female athletes, according to a study in the April issue of The Journal of Strength and Conditioning Research, official research journal of the National Strength and Conditioning Association. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.
The endurance gain likely reflects the added protein as well as a mix of carbohydrates, compared to a standard "single-carb" drink, according to the study by Erin L. McCleave, M.S., and colleagues of The University of Texas at Austin.
Longer Endurance with Protein Plus Mixed-Carb Supplement
Fourteen trained female cyclists and triathletes were studied on two occasions. After performing a long (three-hour) ride, the women performed an intense ride—averaging 75 percent of aerobic capacity (VO2 max)—until exhaustion. On one ride, the athletes were given a standard six percent carbohydrate supplement containing dextrose only. On the other ride, they received a three percent carbohydrate supplement containing a mix of carbohydrates plus 1.2 percent added protein. On each ride, the cyclists were given 275 mL of their assigned beverage every 20 minutes.
The women's time to exhaustion was significantly longer with the mixed-carb plus protein supplement: nearly 50 minutes, compared to 42 minutes with the dextrose-only drink. Thus the mixed-carb plus protein drink increased endurance performance by about 15 percent.
The blood glucose level was also lower with the mixed-carb plus protein supplement. Other metabolic measures—including insulin levels, lactate concentration—were similar between the two drinks.
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," according to 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," McCleave and co-authors conclude. "This may be an important consideration for those individuals concerned about body weight and caloric intake."
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