Cities can play an important role in sparking a shift to a fundamentally different food system in which we move beyond simply reducing avoidable food waste to designing out the concept of 'waste' altogether. As the place where most food eventually ends up, cities can ensure inevitable by-products are used at their highest value, transforming them into new products ranging from organic fertilisers and biomaterials to medicine and bioenergy. Rather than a final destination for food, cities can become centres where food by-products are transformed into a broad array of valuable materials, driving new revenue streams in a thriving bioeconomy.