This thesis examines epidemic obesity from a materialist perspective using the concept of metabolism. It develops an ontology of the metabolic body to identify and engage with material exploitations and injustices associated with epidemic obesity that occur at the scale of the individual, the city and the nation. Case studies include a history of weight loss surgery, evolutionary accounts of diabetes and global obesity reports. It uses an actor network theory approach to advocate for a materialist analysis of obesity that accounts for both human and non-human actors.