The definitive guide to fasting, exercise and brain training for improved health, immunity and brain fitness. Harnessing the adaptive cellular stress response. This extensive article provides a foundation for understanding why long-term caloric restriction (fasting), exercise and working-memory based brain training all promote health, immunity and physical and mental performance, in a way that is complementary – sharing the same biological adaptive stress response. Energetic Stressors in Evolution In the environments of our distant ancestors, food was often scarce, and energy