This article explores a theoretical legacy that underpins the ways in which many social scientists come to know and understand obesity. In attempting to distance itself from essentialist discourses, it is not surprising that this literature focuses on the discursive construction of fat bodies rather than the materiality or agency of bodily matter. Ironically, in developing arguments that only critique representations of obesity or fat bodies, social science scholars have maintained and reproduced a central dichotomy of Cartesian thinking – that between social construction and biology. In this article I examine the limitations of social constructionist arguments in obesity/critical fat studies and the implications for ignoring materiality. Through bringing together the theoretical insights of material feminism and obesity science’s attention to maternal nutrition and the fetal origins hypothesis, this article moves beyond the current philosophical impasse, and repositions biological and social constructionist approaches to obesity not as mutually exclusive, but as one of constant interplay and connectedness.