Brian Wright from UC Berkeley attempts to answer that question in a recent review article in the Journal of Economic Perspectives. His provocative answer:
The rises in food prices since 2004 have generated huge wealth transfers to global landholders, agricultural input suppliers, and biofuels producers. The losers have been net consumers of food, including the large numbers of the world's poorest peoples. The cause of this large global redistribution was no perfect storm. Farm from being a natural catastrophe, it was the result of new policies to allow and require increased use of grain and oilseed for production of biofuels. Leading this trend were wealthy countries, initially misinformed about the true global environmental and distributional implications.