Kim Elliott dares anyone to defend US biofuel subsidies:

The assertion by American officials that biofuels have contributed only 2-3 percent to the rise in food prices is consistent with estimates of the impact on food prices in the United States, where most foods are processed and the value of the crop in the final retail product is a tiny fraction. In poor countries, where minimally-processed staple grains make up a much larger share of calories consumed, the impact of recent food prices is much larger.

Nor is it true, as asserted by congressional defenders of ethanol subsidies, that corn-based ethanol cannot have a large effect on food prices because it uses feed corn, which people do not eat. That is true, but people do eat poultry, eggs, and dairy products from animals fed on corn; increased production of corn also means reduced production of other crops, thus raising their prices, and high corn prices lead people to substitute other food products, again putting upward pressure on other crop prices.