Across the developed world, rates of disordered eating are increasing. Formal eating disorders, unhealthy dieting and obesity have all been escalating over the last forty years. Various theoretical models have been proposed to explain this increase. Sociocultural models have drawn attention to features of the social environment, such as the cultural value placed on thinness for women (causing body dissatisfaction, and subsequently, weight-loss attempts), or the hyperavailability of energy dense foods and energy-saving technologies (causing obesity). Individualistic models have identified a variety of genetic and personality factors, such as perfectionism, low self-esteem and thin-ideal intemalisation, that increase vulnerability to disordered eating. However, these two approaches to disordered eating are currently a) incompatible, and b) unable to account for the evidence of social influence in eating behaviour. In this thesis, I propose a social identity analysis of disordered eating behaviour. This conceptualisation is able to parsimoniously incorporate previous findings by attending to the mechanism through which sociocultural phenomena are represented psychologically (via self-categorisation). Across 10 studies and 5 empirical chapters, evidence is presented for this social identity analysis. Firstly, a Dieting Intentions Scale is developed and validated in four studies, such that future dieting behaviour may be adequately measured as a dependent variable in the research. Secondly, two experiments demonstrate that the perception of shared psychological group membership is a necessary condition for social influence in eating behaviour. Thirdly, three studies show that the predictors of dieting intentions are context-dependent, and are determined by an individual's salient self-categorisations. Fourthly and finally, one experiment tests the applicability of the social identity analysis of social influence in a clinical population. The thesis has implications for social-psychological theory, in extending and testing the social identity approach, particularly in the health domain. However, it has greater implications for clinical-psychological theory, in questioning the biomedical model of eating pathology and suggesting new strategies for modifying and preventing disordered eating behaviour. Overall, this thesis provides a strong case for the relevance of the social identity approach to health generally, and eating behaviour in particular
