The human body is made up of about 37 trillion cells. Each one functions as a mini-factory, churning out all of the stuff that keep us alive, from enzymes to neurotransmitters to hormones and everything in between. The calories we eat give the energy that allows us to carry out our tasks. It takes eight liters of cold water to get to a rolling boil in our bodies every day, and our cells consume enough energy to do so. As a result, energy is the currency of life. However, metabolism — the mechanism that regulates energy use – is often misunderstood. It's past time to make a difference. Among the topics covered in these notes are what Tanzanian hunter-gatherers can teach us about human evolution, how sharing food distinguishes humans from monkeys, and why you can eat nothing but candy bars and yet lose weight.