"Eating Well with Canada’s Food Guide" (CFG), Canada’s official dietary guidelines, is designed to address high rates of obesity and diet-related chronic diseases in Canada. This dissertation reports on a qualitative study of the social and ideological actions that the CFG performs. The study draws on concepts from Rhetorical Genre Studies, Science and Technology Studies, and Multimodal Interactional Analysis, and applies them in the analysis of interviews with key informants involved with the latest revision of the CFG and registered dietitians (RDs) working with vulnerable populations, as well as in a rhetorical and multimodal analysis of the guidelines. The findings of the analyses suggest that the CFG relies heavily on the representations typically reserved for scientific evidence from nutrition science, which focus on nutrients rather than on food. In the context of the CFG, these typical scientific representations are used for non-scientific audiences or in non-scientific situations, that is, cease to be scientific and become scientistic. The scientistic representations create rhetorical complexities, such as layers of rhetorical action (rhetorical laminations), and contribute to multiple rhetorical failures of the CFG. The scientistic representations in the CFG and the rhetorical failures they produce influence how RDs conceptualize nutrition, and dominate, rather than facilitate, discussions about healthy eating. As a result, RDs develop new discursive activities whereby they have to rely on additional resources to translate the scientistic representations for people and apply the CFG to their lives. Overall, the study suggests that the CFG, instead of an enabling resource, serves as a limiting document: it limits who can make healthier food choices and how such choices can be made. The study indicates that the CFG, as a rhetorical failure, has not achieved its intended social and ideological goals, or, in other words, has written itself out of usefulness.