Whether we are elite athletes, office workers or students struggling with assignments, we all need energy and we can only optimise our performance with optimal energy levels. And if our energy demand exceeds our energy supply we eventually have to stop. In her NHS and then independent medical practice, Dr Myhill has increasingly specialised in helping patients with pathologically low levels of energy. Through this she has learned of the centrality of having sufficient energy to live well and stay healthy and of balancing energy generation with energy use. In this, her simplest and most readable account of the fundamentals of good health, supported by editor and former patient Craig Robinson, Dr Myhill provides all we need to ensure the energy equation is resolving in our favour.