Exercise Supplementation: Carbs + Protein For High Intensity Endurance Athletes

What bodybuilder already knew, has now been confirmed by a group of scientists from the University of Texas (Ferguson-Stegall, 2010): Carbs alone won't do the trick! In their study Ferguson-Stegall and collegues investigated the effect of a low carbohydrate beverage (50% less total carbohydrate than a carbohydrate-only supplement) with added protein on cycling endurance performance in 15 trained athletes:

[The subjects cycled] on 2 separate occasions  at intensities alternating between 45 and 70% VO2max for 3 hours, after which the workload increased to approximately 74-85% VO2max until exhaustion. Supplements (275 mL) were provided every 20 minutes during exercise, and these consisted of a 3% carbohydrate/1.2% protein supplement (MCP) and a 6% carbohydrate supplement (CHO).[...] for subjects cycling at or below ventilatory threshold (VT) time to exhaustion (TTE) in MCP was significantly greater than for CHO (45.64 +/- 7.38 vs. 35.47 +/- 5.94 minutes, respectively, p = 0.006).

Other than common wisdom would tell us high intensity exercise does not require larger amounts of carbohydrates. On the contrary if you cycle at the ventilatory threshold it appears to be wiser to replace 50% of the carbohydrates in your sports beverage by easily digestable protein / amino acids.