Have you heard that junk food is cheaper than fruits and vegetables because of the farm bill? It sure seems reasonable, because the ingredients in the junk — sugar from corn, oil from soy, flour from wheat — benefit from far more subsidy money than broccoli and beets.This truism was repeated last month by arguably the most influential person in the sustainable-food movement, author Michael Pollan. At a D.C. farm bill forum hosted by Rep. Earl Blumenauer (D-Ore.), Pollan, whose work I’m a fan of, held up a package of Twinkies (which cost 99 cents) and a bunch of carrots ($2.99). The Twinkies are a complex food with 39 ingredients, and the carrots are “a very simple bunch of roots,” he said. So why do the carrots cost so much more?“This perverse state of affairs is not the result of the free market,” said Pollan, author of “Cooked,” “The Omnivore’s Dilemma” and other influential books. “It has more to do, in fact, with the farm bill.”The idea that wholesome foods are expensive and junk foods are cheap because of the system of subsidies in the farm bill pervades the conversation about food policy. But that idea has one very big problem. It’s false.