What goes in, must come out: Practice metabolism and the thermodynamic limits of urbanization

Contemporary urban life depends on extensive inflows of energy and materials while displacing waste, depletion, and environmental burdens beyond the city. Although urban metabolism research has documented these flows, it has paid less attention to the everyday social practices through which they are organized and reproduced. This article develops the concept of practice metabolism to bridge critical ecological economics and theories of social practice. Practice metabolism refers to the transformation of matter-energy through everyday activities such as mobility, housing, communication, consumption, and food provision. The article advances four arguments. First, it conceptualizes resources as constitutive conditions of social organization rather than neutral inputs. Second, it shifts the analysis of urban metabolism from aggregate flows to socially organized practices. Third, it interprets everyday practices as thermodynamic processes that transform low-entropy resources into high-entropy waste. Fourth, it reframes urban-rural relations as unequal metabolic dependencies sustained through ecologically unequal exchange. By foregrounding the material and energetic dimensions of practice, the article offers a framework for understanding how urban life reproduces ecological overshoot and socio-ecological injustice. It concludes that sustainability requires not only technological improvement but also the reorganization of practices toward lower matter-energy throughput and more equitable metabolic relations.