How the World Really Works: A Scientist’s Guide to Our Past, Present and Future

by Vaclav Smil

lying prone all day a 70-kilogram man would still need about 7 megajoules (80 × 24 × 3,600) of food energy, or about 1,650 kilocalories, to maintain his body temperature, energize his beating heart, and run myriad enzymatic reactions.