^ Fraga, Helder; Malheiro, Aureliano C.; Moutinho-Pereira, José; Cardoso, Rita M.; Soares, Pedro M. M.; Cancela, Javier J.; Pinto, Joaquim G.; Santos, João A.; et al. (24 September 2014). "Integrated Analysis of Climate, Soil, Topography and Vegetative Growth in Iberian Viticultural Regions". PLoS ONE. 9 (9): e108078. doi:10.1371/journal.pone.0108078. PMC 4176712. PMID 25251495.
Most food has its origin in plants. Some food is obtained directly from plants; but even animals that are used as food sources are raised by feeding them food derived from plants. Cereal grain is a staple food that provides more food energy worldwide than any other type of crop. Corn (maize), wheat, and rice – in all of their varieties – account for 87% of all grain production worldwide. Most of the grain that is produced worldwide is fed to livestock.