The paper focuses on the issue of obesi- ty, which has become one of the most insidious world epidemics and a serious threat to global health. The aim is to highlight the relationships between obesity and the sustainability of the food system and to discuss the effectiveness of different policies that could be implemented to address the problem. An empirical analysis has been carried out, aimed at assessing the relationship between price and energy density of foods and price premium for low-calorie foods. The main conclusion of the paper is that the aim of reducing obesity, which is a priority for food sustainability policies, cannot be achieved without regulatory intervention designed to reverse relative prices between obesogenic and healthy foods.