[Protein in the athlete's diet: rationale for intake levels at different training intensities to maintain lean body mass (a brief review)].

Nutrition in sports, as a branch of nutritional science, is a constantly developing field with a growing number of scientific researches and recommendations concerning the justification of the diet composition to ensure the requirements for macro- and micronutrients of the athlete's body at different stages of sports activity and energy value, as well as the use of special dietary supplements of various nature, including protein in forms of specialized dry mixes, drinks, etc. The aim of the research was to present the results of studies conducted abroad, presented in review publications and original articles, on the role of protein and the impact of its various levels of consumption on the maintenance of muscle mass as a criterion for the effectiveness of diets used, including in conditions of their reduced calorie content; on the safety of consuming significantly higher than recommended amounts of protein (>2.0 g/kg of body weight per day); about the relationship between protein dose and the possible increase in lean body mass. Material and methods . For the main source search, the PubMed Internet resource was used, and the websites of the Springer and Elsevier publishers were used to access the full text of the articles. Search depth 10 years. Results . This review presents the official position of the International Society of Sports Nutrition (ISSN) on the role of protein in training optimization, body composition change and improving the performance of athletes. Generalized data on the body's energy costs for the assimilation of nutrients, food thermogenesis and the importance of protein for maintaining resting energy expenditure are presented. Published results based on meta-analyses support the efficacy of higher protein intake in reducing body weight and fat mass while maintaining lean mass in an energy-deficient setting. The anabolic properties of protein under conditions of increased physical exertion will manifest themselves only with sufficient energy and protein supply. The proposed values and boundaries within which increased protein intake effectively affect body composition in the process of adaptation to strength training are given. It has been shown that an increase in protein intake above the average maximum values practically does not lead to an increase in lean body mass without the simultaneous introduction of additional resistance exercises that restores its growth. In accordance with the official position of the ISSN, the recommended protein intake corresponds to values from 1.4 to 2.0 g/kg of body weight per day for individuals performing various special sets of physical exercises. The use of high-protein diets (protein >2.0 g/kg/day) in highly qualified athletes who do not have kidney and liver diseases showed no changes in the biochemical parameters of blood and bone mineral density confirming its safety. Conclusion . Based on the analysis of scientific data, it can be stated that proteins make the main contribution to the thermogenesis of the body compared to other dietary macronutrients. The effect of protein intake on body composition, recovery and muscle building of an athlete has been proven. Athletes require higher amounts of protein to optimal increase of lean body mass under increased training loads and to maintain lean mass under an energy-deficient diet. If necessary, high-protein diets can be used in highly qualified athletes without kidney or liver diseases, but comprehensive researches in this direction should be continued.