Energy, carbohydrates and fats in clinical sports nutrition

Energy metabolism plays a central role in supporting physical activity and athletic performance. In almost all forms of exercise different metabolic pathways and energy systems are used concurrently, with their relative contributions depending on exercise intensity, duration, fuel availability, environment, and physiological adaptations. Carbohydrates and fats both serve as the primary energy sources, with fat dominating during rest and low-intensity exercise, and carbohydrates becoming a preferential fuel at moderate to high exercise intensities. With longer duration of exercise, muscle energy stores become gradually depleted and blood glucose and adipose tissue derived fatty acids become increasingly important sources of energy. Prolonged exercise performance can be enhanced with exogenous carbohydrate supplementation in form of drinks, gels or snacks. Maintaining adequate energy and carbohydrate availability is crucial to support training and recovery and to prevent negative health consequences. While low-carbohydrate, high-fat diets may increase fat oxidation, they often impair performance at higher intensities. Individualised and periodised nutritional strategies that tailor energy and macronutrient intakes to meet the daily requirements of an active individual are essential to optimise health, support adaptations to exercise, and achieve training goals.