More than 240 kilograms of corn — enough to feed one person for a year — is required to produce 100 litres of ethanol.
With the cost of corn already pushing up food prices, a spokesman for the Grocery Manufacturers Association called the projection alarming.
The US Government's ethanol drive may have boosted the fortunes of corn farmers.
About 1500 activists, led by radical French farmer Jose Bove, have ripped up a field of transgenic corn in south-west France.
The women making blue corn tostadas knead the dough before flattening it, their palms bright blue.