Martínez-Lagunas, V, Ding, Z, Bernard, JR, Wang, B, and Ivy, JL. Added protein maintains efficacy of a low-carbohydrate sports drink. J Strength Cond Res 24(1): 48-59, 2010-The purpose of the present study was to investigate the aerobic capacity characteristics of an isocaloric carbohydrate (CHO) plus protein (PRO) drink and a low-calorie CHO plus PRO drink against a traditional 6% CHO sports beverage. Twelve male and female trained cyclists exercised on 4 separate occasions at intensities that varied between 55 and 75% o2max for 2.5 hours and then at 80% o2max until fatigued. Supplements (255.4 ± 9.1 mL) were provided every 20 minutes and consisted of a 4.5% carbohydrate plus 1.15% protein complex (CHO/PRO H), a 3% carbohydrate plus 0.75% protein complex (CHO/PRO L), a 6% carbohydrate supplement (CHO), or a placebo (PLA). Time to fatigue at 80% o2max was significantly longer (p < 0.05) during the CHO (26.9 ± 6.1 minutes, mean ± SE), the CHO/PRO H (30.5 ± 5.9 minutes), and the CHO/PRO L (28.9 ± 6.5 minutes) trials compared with the PLA trial (14.7 ± 3.4 minutes), with no significant differences among the CHO, CHO/PRO H, and CHO/PRO L treatments. In general, blood glucose, plasma insulin, and carbohydrate oxidation were elevated above PLA during the CHO, CHO/PRO H, and CHO/PRO L trials, whereas plasma free fatty acids, rating of perceived exertion, and fat oxidation values were lower during the CHO, CHO/PRO H, and CHO/PRO L trials compared with the PLA trial. Only minor differences in blood parameters occurred among the CHO, CHO/PRO H, and CHO/PRO L treatments. In summary, partially substituting PRO for CHO in a sports drink did not enhance aerobic capacity, but substitution was able to occur without loss of efficacy. Thus, adding PRO to a low-calorie CHO sports drink may be an effective strategy to enhance aerobic capacity while limiting carbohydrate and caloric consumption.
Department of Kinesiology and Health Education, The University of Texas at Austin Exercise Physiology and Metabolism Laboratory, Austin, Texas
Address correspondence to John L. Ivy, email@example.com.