This research explores the implications of ketosis and protein loading, as induced by the Dukan Diet, on endurance in competitive sports. The Dukan Diet, known for its high-protein, low-carbohydrate approach, promotes a metabolic state where the body uses fat as its primary energy source. This shift to fat oxidation has potential benefits for endurance athletes, particularly those involved in ultra-endurance sports. The study examines how ketosis conserves glycogen stores and enhances fat metabolism, offering sustained energy for long-duration activities. However, the research also highlights the challenges athletes face with carbohydrate restriction, especially during high-intensity efforts that depend on glycogen. The role of protein loading in muscle preservation and recovery is discussed, along with the diet's long-term sustainability and psychological impacts on athletes. The findings suggest that while the Dukan Diet may benefit endurance performance, its restrictive nature and the potential trade-offs between fat and glycogen metabolism raise important considerations for athletes seeking to optimize both endurance and high-intensity performance.