Endurance athletes require approximately 1.8 grams of protein per kilogram of body weight per day to support muscle repair, mitochondrial adaptation, and recovery after high-intensity training, and protein requirements exceed 2.0 g/kg/day during carbohydrate-restricted periods due to the contribution of protein oxidation to energy metabolism during prolonged exercise.

When endurance athletes train hard, their muscles break down and their energy stores run low. Eating enough protein gives the body the building blocks it needs to fix muscle damage and make more energy-producing parts inside cells. Amino acids from protein turn on signals that build new muscle and mitochondria, and when carbs are low, the body burns some of those amino acids for energy, which means more protein is needed to keep up with repair and adaptation.