Phosphorus is required as a fertilizer for producing food, and there is no substitute. Losses between mine production and diet result in significant environmental harm. We used a demand-driven substance flow model to explore the sensitivity of global phosphorus production to interventions of the food system including: reduction in animal fraction in the diet (AFD); manure use efficiency (MUE); animal food yield (YA); phosphorus use efficiency (PUE); the fraction of food that is wasted (FWF); the fraction of food waste recycled (FRE); and the fraction of human waste recycled (WRE). The model indicated that AFD and YA are the most influential interventions, and they interact with PUE and MUE. Furthermore, there is a minimum in AFD and YA below which it becomes necessary to increase mining. Another result is that reducing food waste is about 80 times more effective than recycling food waste in reducing P demand. Finally, the model was used to explore the global carrying capacity for humans on the basis of P sources other than mining. These sources may satisfy P requirements for as many as 2.5 billion people. If significant improvements were made in all of the considered interventions simultaneously, as many as 14.7 billion people could be sustained.