Modern industries exhibit a systemic disconnect in the management of carbon resources across sectors that contributes to disproportionately high greenhouse gas emissions. The food sector, for example, discards protein-rich side streams and carbohydrate-rich waste that could be converted into renewable carbon feedstocks, whereas the manufacturing sector consumes non-renewable, petroleum-based carbon feedstocks for material synthesis. This Review examines valorization routes that could address this imbalance by transforming proteins extracted from food side streams or created by fungal bioconversion of carbohydrate-rich food waste into feedstocks that enable the production of sustainable materials for packaging, water purification, CO2 capture and energy conversion, as well as surface-engineered applications such as coatings, biosensors and emulsifiers. At the end of their useful or service life, these materials (unlike those recycled using conventional linear approaches) can be repeatedly recycled via depolymerization into amino acids and reassembly into new proteins to yield new material feedstocks. Embedding ‘safe and sustainable by design’ principles into the early stages of material development further ensures that environmental and societal considerations are integrated throughout the material’s life cycle. Together, these advances define a nature-inspired circular-economy material recycling framework grounded in scalable innovation, molecular renewal and upcycling that positions proteins as key to closing the carbon loop.