To eat corn directly (as Mexicans and many Africans do) is to consume all the energy in that corn, but when you feed that corn to a steer or a chicken, 90 percent of its energy is lost—to bones or feathers or fur, to living and metabolizing as a steer or chicken. This is why vegetarians advocate eating “low on the food chain” every step up the chain reduces the amount of food energy by a factor of ten, which is why in any ecosystem there are only a fraction as many predators as there are prey.
