Debates about obesity in bioethics tend to unfold in predictable epicycles between individual choices and behaviours (e.g., restraint, diet, exercise) and the oppressive socio-economic structures constraining them (e.g., food deserts, advertising). Here, we argue that recent work from two cutting-edge research programmes in microbiology and social psychology can advance this conceptual stalemate in the literature. We begin in section 1 by discussing two promising lines of obesity research involving the human microbiome and relationship partners. Then, in section 2, we show how this research has made viable novel strategies for fighting obesity, including microbial therapies and dyad-level interventions. Finally, in section 3, we consider objections to our account and conclude by arguing that attention to the most immediate features of our biological and social environment offers a middle ground solution, while also raising important new issues for bioethicists.