An alternative to the current linear paradigm is to develop productive systems that minimise external inputs, pollution and waste (as well as risk, dependency and costs) by adopting a circular metabolism. There are two principles here, both reflecting the natural world. The first is that natural systems are based on cycles, for example water, nitrogen and carbon. Secondly, there is very little waste in natural systems. The ‘waste’ from one species is food for another, or is converted into a useful form by natural processes and cycles.