The undernutrition and obesity pandemics associated with climate change are a global syndemic. They have a point of convergence, which is the unsustainable current food systems. This paper aims to discuss the role of public health policies, particularly the Brazilian Unified Health System (SUS) in the context of Primary Health Care, in combating the global syndemic and in the development of sustainable food systems. In this scenario, the National Food and Nutrition Policy is a leading intersectoral tool for an adequate and healthy diet and food and nutrition security. Also, the Dietary Guidelines for the Brazilian population is a strategic tool to support food and nutrition education. We highlight the need to articulate health, agriculture, and environmental policies to achieve sustainable development. Thus, SUS can be the arena to promote the main discussions on this topic, potentiating individual, group, and institutional actions to provide a fairer, healthy, and sustainable food system.