UNEP estimates the effects of feeding cereals to animals instead of humans
"The United Nations Environmental Programme (UNEP) estimates that, even accounting for the energy value of the meat produced, the loss of calories that result from feeding cereals to animals instead of using cereals directly as human food represents the annual calorie need for more than 3.5 billion people. In addition, food losses in the field (between planting and harvesting) may be as high as 20 to 40 per cent of the potential harvest in developing countries, due to pests and pathogens, and the average post-harvest losses, resulting from poor storage and conservation, amount at least to 12 per cent, and up to 50 per cent for fruits and vegetables."
Oliver De Schutter. "Report submitted by the Special Rapporteur on the right to food". Human Rights Council, A/HRC/16/49: 4 [verified 4/15/14]