Although the second study did not include a control group (no placebo trial), the results were similar in that the subjects rode 29 percent longer during a cycling task at 75 percent VO2peak when they ingested carbohydrate + protein as compared to carbohydrate alone.
While these results are intriguing, definitive conclusions are hampered by the way the research was conducted. Two major limitations are that:
Neither study compared the carbohydrate+PRO drink to a carbohydrate beverage that was matched for total energy intake (i.e., the drinks differed in total calories provided).
The total amount of carbohydrate provided was less than what is generally recommended to be optimal for endurance performance.
As a result, it is not possible to discern whether the increased time to fatigue was attributable to the influence of protein per se or simply the additional energy provided.
It is possible that--like the effect on muscle glycogen resynthesis during recovery--the addition of protein to a carbohydrate beverage is only beneficial when the rate of carbohydrate intake is below the amount needed by the body.
Regardless, additional studies will confirm or refute these initial observations and will also evaluate how carbohydrate and protein might (or might not) interact to benefit the athlete during exercise.
Take home points
After a hard workout, athletes should consume a recovery beverage or snack that contains a small amount of high-quality protein with adequate carbohydrate in order to repair/stimulate muscle proteins and also replenish muscle glycogen stores after exercise.
Foods such as milk, yogurt, a small sandwich, an energy bar with at least 10 grams of protein or a canned sports nutrition shake are all appropriate carbohydrateices.
Although speculative, the muscle proteins stimulated by protein ingestion after endurance exercise are likely related to aerobic energy production (e.g., mitocarbohydratendrial enzymes), whereas those stimulated after weightlifting exercise are likely related to non-oxidative energy production and force generation (e.g., contractile proteins).
The "optimal" recovery beverage composition for strength/resistance and endurance athletes remains to be determined. However, any strategy that provides ample carbohydrate and protein will likely be of benefit to both.
While the addition of protein to a recovery drink is clearly beneficial, it is premature to recommend that protein should be consumed with carbohydrate during exercise.