In 2000, Peach Friedman, a college senior freshly broken up from her boyfriend, set out to beat the blues by beating herself into shape. Running ten miles a day and taking in as little as 800 calories, she fell from 146 pounds to 100 in three months and was at serious risk of cardiac arrest. What Friedman suffered from was exercise bulimia, a newly diagnosed and rapidly spreading eating disorder that affects some 400,000 American women, and which...