For many years, athletes were advised to consume very high levels of carbohydrates, with little attention placed on the amount and timing of the protein they consumed. Personally I was very much a proponent of this sort of regimen for athletes. I worked in the sports nutrition arena for years, and provided diet and exercise advice to many professional and college athletes.
But times change, and the science supporting carbohydrate as the near-exclusive domain of athletes has changed as well. Im not suggesting that carbs are no longer considered a key substrate for athletes; quite the contrary, carbohydrates provide the quick energy that athletes need, and they allow athletes to use their other energy substrates (fats and proteins) effectively. But newer research indicates that athletes need more protein than previously believed; about 1.5 to 2 times as much. As we learn more about the role of amino acids as messengers in various metabolic pathways, weve come to appreciate the need for protein to provide ample levels of these amino acids to promote, among other things, optimal muscle growth and repair. And newer studies suggest we wont achieve ample amounts of particular amino acids (e.g., leucine) on RDA-levels of protein. Further, on a more applied note, studies such as those by John Ivy at the University of Texas and others have indicated that an appropriate ratio of carbohydrate to protein (somewhere in the neighborhood of 3:1 carb:protein) may be better at enhancing post exercise recovery than consuming carbohydrate alone.
Here is an article that serves as a basic primer on some of the newer research on protein and exercise. While some of this work is in preliminary stages, and we still have more to learn about the effects of various substrates on exercise performance, suggesting that athletes increase their protein intake a bit (largely through food) is sound advice. Carbohydrates are still important, but the role of protein in physical activity should not be underestimated.