In recent years, significant attention has been given in the popular and academic press to an ‘obesity crisis’ that, purportedly, is both ever increasing and sweeping across the western world. In this paper, we raise a number of ethical issues about the ways in which discourses around this crisis have been socially constructed and publicly represented. We begin by outlining the ways in which these discourses seem to offer ‘certainty’ and ‘authority’ (of ‘fact’ and knowledge) from within the research field. Yet, as others have pointed out, on closer inspection few such certainties are to be found. We argue that attempts to erase uncertainty around the body, health and size/weight/fatness may be ethically problematic, not least because it can lead to forms of size discrimination and oppression that, ironically, may propel some people towards ill-health via disordered relationships with food, exercise and the body.