The modern food system no longer relies on these energy-efficient foods. It is based instead on the highly inefficient conversion of complex carbohydrates, often in the form of grains and beans, into animal protein and fat. Feeding these valuable foodstuffs to livestock and then eating them in the form of animal food wastes a tremendous amount of raw materials and energy. One expert estimated that if the world were to adopt these methods of food production, all of the known reserves of petroleum would be exhausted in thirteen years. Modern food production contributes a great deal of carbon dioxide and other greenhouse gases to the atmosphere.
Cattle ranching, for example, is the single largest source of methane, a leading greenhouse gas.
Whole grains, beans, and vegetables are far more energy-efficient than animal products. Corn or wheat return 22 times more protein per calorie of fossil fuel expended than does beef produced on the modern feedlot. Soybeans are 40 times more energy efficient than modern beef. In Diet for a New America , John Robbins describes the energy savings that would result from a shift toward whole grains, beans, and vegetables. And, the supply of renewable energy, such as wood and hydroelectric, would increase 120 to 150 percent.