The aim of this study was to determine the association between eating behaviours, sedentary behaviours and physical activity based on a self-reported survey conducted on a sample of the Polish population of adolescents aged 13–16. The field survey was conducted on a nationwide group of 6818 respondents. The object of the statistical analysis was to develop a model regarding the influence of selected socio-demographic characteristics on engaging in physical activity and selected dietary behaviours. Due to the dichotomous nature of the dependent variable, logistic regression models were used in the model. It was found that the higher the level of physical activity, the more well-balanced the diet, including higher levels of fruit consumption, water consumption and protein-containing products, as well as the relatively less frequent occurrence of sedentary behaviour as a form of leisure activity. However, there is a constant need to develop, in cooperation with scientific and research institutions and educational establishments, mechanisms for influencing a change in the behaviour of young people towards a more pro-healthy lifestyle so that the effects of these educational activities are not only reflected in an increase in the level of knowledge in this area but also contribute to real changes in dietary behaviour.