Food security depends on efficient distribution and affordability as well as on sustainable production (Nature 466, 558–560; 2010). We are already seeing the acquisition of African farmland by Asian countries to feed their own populations, and we can expect more dislocation globally between sites of food production and consumption, exacerbated by growing urbanization. This will aggravate distribution problems and adversely affect affordability by increasing financial barriers (transport costs) and economic impediments (market distortions).

As well as ecological indicators of sustainable food production, we need metrics to track socio-economic factors affecting affordability and distribution gaps.