Food as an energy source is actually an important aspect. Things like domesticated animals represent significant sources of energy, on the order of thousands of

Food as an energy source is actually an important aspect. Things like domesticated animals represent significant sources of energy, on the order of thousands of calories per day. More nutritious crops also confer a significant boost to available energy. This had significant impact on the disparate levels of development between Eurasia and the Americas before the early modern period. "The Measure of Civilization" by Ian Morris is a book I'd recommend on this topic.