How does regular exercise protect against mental decline?

A study published online Aug. 20, 2021, by Nature Metabolism suggests that the hormone irisin, produced during exercise, might have something to do with the beneficial effects of exercise on the brain. Scientists suspect that irisin plays a role protecting the brain against changes characteristic of Alzheimer’s disease, possibly by reducing brain inflammation. Irisin has also been shown to turn white fat cells (which store fat) into brown fat cells (which burn fat), and also to improve insulin resistance. Such changes reduce body weight and protect against both diabetes and heart disease.