(Sayer Ji) The energy needs of the human body have long been envisioned as dependent upon physical “fuel” being fed to the glucose-burning furnaces within the mitochondria of our cells. Indeed, our fixation on the caloric content of food reflects this outdated and fundamentally inaccurate concept. Calories are simply a measurement of the amount of heat given off when we internally incinerate food, which is a crude metric when we consider the complexity, elegance, and mystery of human metabolism.