This article argues that public health campaigns have an ethical obligation to combat fat stigma, not mobilize it in the “war on obesity.” Fat stigma is conceptualized, and a review is undertaken of how pervasive fat stigma is across the world and across the lifespan. By reviewing the negative impacts of fat stigma on physical health, mental health, and health seeking behaviors, fat stigma is clearly identified as a social determinant of health. Considering the role of fat stigma in public (...) health, and the arguments made for using stigmatisation in public health campaigns to promote population health, it is concluded that it is a violation of public health ethics to use stigma as a tool in combatting fatness. The article concludes by making recommendations of how public health in New Zealand can combat, rather than reinforce, fat stigma. (shrink)