Top results in sport is higly dependent on optimal nutrition. Adequate food and beverage intake is important before, during and after training in order to improve training performance, fluid and electrolyte replenishment, and faster muscle recovery. The duration and intensity of training, the ability to perform, and food consumed before training will influence metabolic energy system that will predominate in the body's energy supply. Metabolic energy systems are divided into aerobic and anaerobic systems differing not only in oxygen usage but also in the rate of energy release and total capacity of the system. The rate of the food energy availability could be described by the glycemic index of a food that is a numerical scale, from 0 to 100, which determines how much and how quickly certain foods raise blood glucose levels. The basis of sports nutrition is sufficient and timely intake of all nutrients, carbohydrates, proteins and fats, as well as micronutrients, ie vitamins and minerals. Supplementation is required in the absence of a single micronutrient. A good hydration plan prevents conditions of dehydration and hyperhydration that adversely affect sports performance.