Your “food” eats oats too. And feed corn. And hay. And probably sorghum and molasses too. Are farmers allowed to use those feedstocks for anything other than livestock feed?
And no need for the scare quotes around the word food. I eat cows, and chickens, and pigs, and turkeys. If you don't, that's your problem.
Allowing and mandating are not the same. Subsidizing and mandating together are not a free market