Trained female athletes were placed on a low carb-and-protein supplement or a moderate carb supplement.
Research in The Journal of Strength Conditioning and Research suggests that a carbohydrate and protein supplement may improve endurance in athletes compared to a supplement of just carbohydrates.
Researchers at the University of Texas-Austin assigned 14 trained female cyclists and triathletes to cycle for three hours at 45–70% oxygen uptake (VO2), and then until exhaustion on two separate occasions. Subjects were assigned to a 275 mL supplement containing carbohydrates and protein (1% dextrose, 1% fructose, 1% maltodextrin, and 1.2% protein) or just carbohydrates (6% dextrose) every 20 minutes during exercise.
Even though the carbohydrate-and-protein supplement was lower in overall carbohydrates, the researchers wanted to see if adding protein would provide a benefit equal or greater than moderate carbohydrates alone.
Adding protein did seem to have a beneficial effect. While blood glucose was significantly lower with the protein-added supplement, average time to exhaustion was significantly greater with protein compared to no protein (49.94 minutes compared to 42.36 minutes).
“It is likely that the greater performance seen with [carbohydrates and protein] was a result of the [carbohydrate-protein] combination and the use of a mixture of [carbohydrate] sources,” concluded the study researchers.