The primary function of carbohydrates in an athlete's diet is to serve as a main energy source. Carbohydrates are broken down into glucose, providing readily available energy for high-intensity and endurance activities. They also help replenish glycogen stores in muscles and the liver, which is critical for optimal performance during prolonged exercise. Athletes are encouraged to consume adequate carbohydrates before, during, and after workouts to maintain energy levels and support recovery, making them an essential component of an effective nutrition strategy.