Psychiatrist John Ratey has called physical activity Miracle-Gro for the brain. The reasons for such a statement are many. Among them: moderate-to-vigorous physical activity “feeds” the brain with oxygen, water, and glucose, which optimizes its performance. (We would never consider depriving our bodies of food for days, weeks, or months at a time; yet when we fail to move, we’re depriving our brains of food.)