In this paper I examine how knowledge claims operating through two types of governance techniques can guide product innovations in the agri-food sector. The notion that knowledge claims have strong social and material components informs the analysis undertaken, developed through a discussion of social science approaches to the role of human groups and biophysical properties in social change. I apply this socio-technical perspective to two case studies: defining dietary fiber and reducing saturated fat. The first involves attempts to produce an international definition of dietary fiber standards in the Codex Alimentarius Commission. The second involves efforts by food manufacturers to reduce the saturated fat content of food products in line with UK government guidelines. The case studies draw upon observations, document analysis, and over forty interviews. I suggest that although knowledge claims are active constituents of both governance processes, important differences are evident and arise from the history of scientific and technical controversies, and from the scope for articulating broader questions. In particular, the different criteria for judging “success” guide how knowledge claims are implicated in the governance of product innovation. I suggest that further work is required to understand the wider implications of efforts to change the composition of foods, not only for public heath, but also in relation to food security, quality, safety, and availability in a rapidly changing context. In order to do this successfully, knowledge claims made about the material properties of food should be made objects of social science analysis.