The Impact of Increased Physical Activity at School on the Nutritional Behavior and BMI of 13-Year-Olds.

: Diet and physical activity (PA) significantly impact health. Unfortunately, a worrying trend of decreasing PA among children and adolescents, accompanied by unhealthy nutritional behavior, is observed worldwide. The aim of the study was to evaluate the nutritional behavior and body mass index (BMI) of adolescents aged 13 years in groups of extended and standard PA at school. : The study was conducted in six schools among adolescents born in 2007 ( = 213), in two groups of standard and extended PA at school (SPA and EPA), wherein each group received 4 and 10 h of physical education lessons per week, respectively. Their height and body mass were measured. BMI was calculated and compared with percentile charts. A questionnaire was used to assess nutritional behavior and extracurricular physical activity. : Approximately 62% of adolescents had a normal body weight, with SPA 58%, EPA 64%, overweight 13.63%, SPA 13.75%, EPA 13.50%, obesity 14.13%, SPA 19.25%, EPA 9%, and underweight 11.17%, SPA 8.85%, and EPA 13.50%. Among the potential health-promoting foods, dishes, and beverages, fruits and vegetables were the most frequently consumed items, whereas fish and legume dishes were the least consumed. Butter, white bread, sweets, cheeses, cold cuts, and sausages were all consumed very often. Fast food and lard were the least frequently consumed items. : A significant proportion of 13-year-olds were overweight or obese. Extended PA had a beneficial effect on BMI, but it had little effect on nutritional behavior among the studied adolescents. The adolescents exhibited moderate nutritional behaviors; however, it was more favorable in those exposed to extended PA at school than those exposed to standard PA. It is possible to argue that extending organized PA at school leads to increased PA during leisure time. It is recommended to increase PA for adolescents by doubling the mandatory number of physical education lessons or other sports activities in the school curriculum.