The World Bank points out that "the grain required to fill the tank of a sports utility vehicle with ethanol ... could feed one person for a year."It is obvious, at least it is to me, that diverting food products to fuel is highly inefficient (it takes 1.3 gallons of fossil based fuel to create a gallon of biofuel) and, on top of driving up food costs, creates grain shortages in the parts of the world most dependent on grain for food.
Mr. Monbiot also suggests that the feeding of grain to animals is inefficient and adds to the shortage. This is no doubt correct, though I would question his conversion rate for beef animals. He cites a rate of some 8:1 and from what I remember from my animal science education, it was close to 3:1 thirty years ago, surely it is somewhat improved now. But it is not just meat production that requires grain. Dairy is perhaps the area where an 8:1 conversion rate applies, and even vegetarians (though not vegans) like milk and cheese.
He is not condoning a vegan lifestyle as it is clearly not a healthy route. Humans have not developed as vegans. Meat has been a part of the species diet for 500,000 years, so it is unlikely that the human omnivore can successfully convert to a vegan in even a few generations.
Of course we can eat range fed beef. This takes no grain production from the human food chain. Mr. Monbiot takes issue with this, as bovine flatulence and belching add, by his citation, 18% of the carbon dioxide to the atmosphere, and he is apparently a global warming enthusiast. Range fed beef would be a good trade off as it not only does not use grain stocks, but it is less fatty and therefore should not contribute as heavily to coronary artery disease.
I don't have a solution for a potential food shortage, but I cannot fathom why we would convert food to fuel when there is still a highly adequate supply of fossil fuels. Seeking alternative energy sources is good and should be done, but not at the expense of people who need grain just to survive. Biofuel is not an energy plan, it is just feel good activity for people who don't think through the whole system.