Research on urban metabolism (UM) focuses on cities' material and energy systems by identifying paths and transformation processes of all kinds of flows in urban contexts. In particular, scientific studies aim to trace the origin and destination of materials, energy, water, emissions and waste flows in order to understand relationships between cities and other spatial areas (hinterlands) that lead to political, social and environment consequences. This research paper aims to analyze complex power relationships between cities and their hinterlands. In particular, the objective is to understand the nature of these socio-material links. Are they based on synergies and cooperation, or, on the contrary, on unbalanced power and conflicts? We propose an approach which combines methodologies with the tools of Energy Flow Analysis (EFA) and semi-structured interviews, in order to develop a “political-industrial ecology” of energy metabolism (Breetz 2017; Cousins and Newell 2015). We have studied the Saint-Nazaire metropolitan area, which is constituted by an urban area and a port zone. This harbor consists in a complex network of highly energy-intensive industrial sites operating in the steel, petrochemical and agri-food industries. Based on an analysis of energy flows, institutional policies and professional practices, we have identified several situations of metabolic links that exist simultaneously. In conclusion, the metabolic relationships' framework is useful to understand how the “hinterlands-city” relationships shape and are shaped by the city's metabolism.