Nutrition of athletes is important in achieving the best results possible. Emphasis in an athlete's diet is placed on carefully planned type, quality and ratio of nutrients. A high proportion of carbohydrate, moderate amounts of fat and low protein intake are the foundation in the nutrition of athletes. Micronutrients, vitamins and minerals, need to be carefully balanced for health reasons, but also because of adequate sports performance. In case of shortage of individual micronutrients their supplementation is necessary. Satisfying the energy needs of an organism is the priority in athletic nutrition. Recommended daily energy intake varies individually and it depends on gender, age, height, weight and physical activity throughout the day. Selection of high quality nutrients must begin as early as during childhood in order to ensure proper growth and development of the organism. Ratio of entered nutrients varies depending on the type of sport that the athlete does, whether it is a sport in which the key is endurance or muscular strength. Food intake before training is proven to enhance the ability to perform training. During the training intake of water and electrolytes is crucial, which is achieved with abundant hydration and sports drinks which contain 6-8% carbohydrate. After training athletes have to compensate consumed glycogen reserves, which requires a meal rich in carbohydrates, but if there is a need to achieve anabolic effect on muscles, meal must also be rich in protein. Optimal hydration is an important factor of success in sports competition. Dehydration is considered to be a loss of liquid in the amount of 2-3% of body weight. Dehydration compromises the performance during aerobic exercise and increases the risk of potentially fatal heat conditions such as heat stroke.