Effect of a low carbohydrate - moderate protein supplement on endurance performance in female athletes

The purpose of this study was to investigate if a low mixed carbohydrate plus moderate protein supplement, provided during endurance exercise, would improve time to exhaustion in comparison to a traditional 6% carbohydrate supplement in female athletes exercising at or below their ventilatory threshold. Fourteen (n = 14) trained female cyclists and triathletes cycled on two separate occasions for three hours at intensities varying between 45% - 70% VO₂max, followed by a ride to exhaustion at an intensity approximating the individual's VT (average 75.06% VO₂max). Supplements (275ml) were provided every 20 min during exercise and were composed of a 3% carbohydrate mixture + 1.2% protein (CHO+PRO) or a 6% carbohydrate-only (CHO). The CHO+PRO treatment contained a mixture of dextrose, maltodextrin, fructose, and whey protein isolate. The CHO treatment was composed of dextrose only. Time to exhaustion (TTE) was significantly greater with CHO+PRO in comparison to CHO (49.94 ± 7.01 vs 42.36 ± 6.21 min, respectively, p < 0.05). Blood glucose was signifcantly lower during the CHO+PRO (4.07 ± 0.12 mmol x L⁻¹) trial compared to CHO (4.47 ± 0.12 mmol x L⁻¹), with treatment x time interactions occurring from 118 minutes of exercise until exhaustion (p < 0.05). Heart rate was significantly lowered in the CHO+PRO treatment during exercise as compared to CHO (p < 0.05). There were no significant differences for other blood measures, ratings of perceived exertion or carbohydrate and fat oxidation between trials. Results from the present study suggest that the addition of a moderate amount of protein to a low mixed carbohydrate supplement improves endurance performance in females above that of a traditional 6% carbohydrate supplement. Improvement in performance occurred despite CHO+PRO containing a lower carbohydrate and caloric content. It is likely the greater performance seen with CHO+PRO was a result of the carbohydrate protein combination and the use of a mixture of carbohydrate sources.