Food security is increasingly a societal concern, also in developed economies. While originally developed through a nutritional lens, food security is also increasingly incorporating the environmental quality of diets. This study develops a Structural Equation Model to examine how consumers concerns over food insecurity – in terms of its impact on health and poverty – and environmental beliefs influence the carbon footprint of diets. Using data from a survey representative of the Italian population, this study shows that health-related food insecurity concerns increase the use of health motives when shopping for food, in turn reducing the carbon footprint of the diet. Conversely, poverty-related food insecurity concerns are associated to diets higher in carbon footprint, as they reduce health motives, and increase private shopping motives (e.g., taste, low price). Overall, the study highlights how shifts to more sustainable food systems require a better understanding of what motivate consumers to make more sustainable food choices.