The European Union relies on imports to meet the protein requirements of its livestock. Regions specialized in livestock production suffer even more from a deficit in protein self-sufficiency. Legumes represent an interesting source of plant protein. However, despite public policies promoting legume production, their use in animal feed remains limited. The aim of this study was to define levers to increase protein self-sufficiency in western France with a view to reducing negative environmental impacts of agricultural production. A regional foresight was performed to define innovative levers for legume production, which could improve protein self-sufficiency. Then, a modeling framework was developed to assess economic and environmental impacts of different levers. It combines a Computable Generable Equilibrium model and the regional model SYNERGY, which simulates local exchanges of crops between farms. Results showed that an increase in coupled support for legumes leads to an increase in legume production but has no influence on protein self-sufficiency or other indicators, since legumes are not used in greater amounts in feed. When the demand for GMO-free animal products increases, the production of legumes, including multispecies grassland, increases substantially, and most livestock are fed legumes. However, on pig farms, protein self-sufficiency decreases because legume production does not meet the quantity needed by pig rations. Local exchange of crops between farms was limited. Regional profit increases, but environmental indicators do not improve, in part due to the increase in legume imports from outside western France. In such a highly specialized region, improvement in protein self-sufficiency seems relatively limited, and a decrease in livestock production should be considered to meet this objective and improve environmental results.