Early organisms existed in harsh environments with stressors such as food scarcity and predation. Adaptive responses to stressors such as increased neural activity while fasted, promoted survival. Dr. Mattson contends that unstressed cells become complacent, making them more vulnerable to the stressors that cause disease, including oxidative stress and inflammation. In modern times, fasting and exercise are behaviors that mildly stress cells. Exercise promotes resilience, stimulates antioxidant defenses, and increases autophagy, the removal of damaged proteins and dysfunctional organelles. Researchers in Dr. Mattson's laboratory observed that animals that were fasted or exercised had increased the number of mitochondria and increased the number of synapses in the animal's brain. In this clip, Dr. Mark Mattson describes the importance of transient, short-term, mild energetic stress to maintain healthy cells.