“Exercise turns out to be the closest thing to a wonder drug that self-control scientists have discovered. For starters, the willpower benefits of exercise are immediate. Fifteen minutes on a treadmill reduces cravings, as seen when researchers try to tempt dieters with chocolate and smokers with cigarettes. The long-term effects of exercise are even more impressive. It not only relieves ordinary, everyday stress, but it’s as powerful an antidepressant as Prozac. Working out also enhances the biology of self-control by increasing baseline heart rate variability and training the brain. When neuroscientists have peered inside the brains of new exercisers, they have seen increases in both gray matter—brain cells—and white matter, the insulation on brain cells that helps them communicate quickly and efficiently with each other. Physical exercise—like meditation—makes your brain bigger and faster, and the prefrontal cortex shows the largest training effect.” - Kelly McGonigal