Introduction: The obesity epidemic has begun in the 80s and is still spreading which makes it a serious social and medical problem for the contemporary world. WHO stated that obesity is a chronic disease which requires complex treatment (special diet, change in a life style, physical activity). Both, individual workout performed on the aerobic equipment and resistance training, are crucial for obesity treatment. Propagating healthy lifestyle and proper eating habits among the whole nation is the basis for preventing and curing obesity and overweight. Aim of paper: The aim of the research was to evaluate the diet and the body composition in a group of adolescence, aged 16-18 beginning yearly professionally designed fitness program. Material and methods: The group of 90 girls and 64 boys began a specially designed fitness program which lasted 12 months. The nutritional state together with the body composition was evaluated with the use of bioelectrical impedance method (equipment InBody 220, producer Biospace). Results: The average BMI of the beforehand mentioned group was 23.3 [kg/m2] in girls and 24.4 [kg/m2] in boys. Although the BMI was close to normal the average amount of body fat was too high in girls (28.7%). In the group of girls the BMI showed a proper weight, however the amount of body fat was too high, it was suggested that the amount of fat tissue was decreased while the amount of skeletal muscles was increased. These data show that the proper body proportions were shaken. Conclusions: Professional equipment used for evaluation of the body composition helps to create a detailed program for fat reduction and muscle tissue growth together with creating a professional individual training program.