Young high-level athletes are frequently exposed to deficiencies, the most frequent origin of which is dietary. Supervision must be clinical, biological and dietary. Recommendations should be made individually, based on the nature and intensity of the exercise, and are calculated from the recommended supplements for the paediatric population. Protein, glucid and lipid supplements must represent approximately 12, 60 and 28% of the daily energetic intake respectively, the glucid ratio reaching 70% under certain conditions of prolonged exercise. Liquids must be controlled when exercise takes place in a warm atmosphere because young athletes are rapidly exposed to dehydration, the osmolarity of the selected drink being below 250 mosm/l. Mineral and vitamin supplementations are recommended. For minerals, perspiration losses may be associated with dietary deficiency. Possible vitamin deficiencies concern B1, B2, B6, B9, B12, C and D vitamins. The daily mineral supplements are estimated at 10 mg for iron, 5 mg for zinc and 1 mg for copper, and have to be prescribed in regular treatment after biological control.