As other pointed out here, the world of athletic sports is quite wide and therefore the diets of many athletes are varied.
As a general rule of thumb, Id assume that most high performance athletes gets the majority of their calorie from carbohydrates. Carbohydrates are an easily and readily available source of energy for the body, and because high intensity exercises require high energy, carbs are the most reliable way to ensure you won't be running on empty. This goes for athletes who train long all day, everyday.
On the other hand, id bet that athletes like body builders have quite different diet. People who focus on building muscle over cardio vascular endurance don't really need to focus on fueling energy reserves. Many professional body builders only workout for an hour at most, several times a week, since body building is more about recovery and diet than intensive, endurance training. Because they're trying to fuel muscle recovery, they most likely have diets which emphazise protein over carbohydrates in order to maximize muscle growth and minimize body fats.