(1) Background: Diet and physical activity (PA) significantly impact health. The aim of this study was to evaluate the impact of long-term increase in organized PA level at school on the eating behaviour and leisure time of early adolescences in the period from the age of 10 to 12. (2) Methods: Children born in 2007 (n = 278) in groups with a standard (control group) and increased level of organized PA at school (4 and 10 h a week) were subjected to an anonymous follow-up survey. The questionnaire included 22 questions related to the eating behaviour and ways and frequency of leisure time PA. The study was conducted in the same groups in three assessment sessions in September 2017, 2018 and 2019. (3) Results: During the course of the study, it was shown improvement of eating behaviour in the increased PA group whereas decline in the standard PA one. The share of children with good and very good scores of eating behaviour decreased in the standard PA group from 56.89% to 54.54% and increased in the increased PA from 58.06% to 60.29%. In the increased PA group children more frequently than standard PA ate vegetables, fruits, fish, poultry meat, wholemeal bakery products, milk, dairy products and drinking tea without sugar, as well as ate breakfast. The standard PA children more frequently than increased PA ate high sugar and/or fat content food as sweets, savoury snacks and drank fizzy drinks as well as fast foods. The frequency of often undertaken leisure time PA increased in the increased PA group from 67% to 74%, while decreased in the standard PA from 58% to 52%. (4) Conclusions: Increase in organized PA at school beneficially influenced early adolescents' eating behaviour and frequency of leisure time PA during 2 years observation. It also increased early adolescents' awareness of healthy diet. Increased PA at school helps shaping healthy lifestyle among early adolescents.
Keywords: adolescence; eating behaviour; lifestyle; physical activity; school-aged children.