Ensuring sustainable food systems requires vastly reducing its environmental and health costs while making healthy and sustainable food affordable to all. One of the central problems of current food systems is that many of the costs of harmful foods are externalized. At the same time, the benefits of healthful foods are not appreciated. This paper sets out the results of an analysis to determine the current cost of externalities in the food system and the potential impact of a shift in diets to more healthy and sustainable production and consumption patterns.