Did you know that physical exercise may be the closest thing to a wonder drug that self-control scientists have discovered? Fifteen minutes on a treadmill reduces cravings (e.g., seen when researchers try to tempt dieters with chocolate and smokers with cigarettes). According to Kelly McGonigal PhD, author of The Willpower Instinct, the long-terms effects of physical exercises are even more impressive: it relieves everyday stress; is as powerful an antidepressant as Prozac; enhances the biology of selfcontrol by increasing baseline heart rate variability and training the brain; and can increase both gray matter and white matter in the brain. There's no scientific consensus on the amounts needed, however. A 2010 analysis of ten different studies showed that the largest mood-boosting and stress-reducing effects came from five-minute doses of exercise rather than hour-long sessions. (McGonigal, Kelly, PhD. The Willpower Instinct. p 42. NY: Avery, 2012.