Matthew McConaughey and Jared Leto are receiving buzz during awards season for their dramatic transformations in "Dallas Buyers Club." Take a look at some of the other most dramatic actor transformations ever seen on film.
For one of his earliest roles, that of a heroin-addicted soldier in the 1996 film "Courage Under Fire," Damon ate only chicken, egg whites, steamed broccoli and plain baked potatoes for months. He also ran 13 miles in total a day, dropping 40 pounds by the time filming began. He's said he lost so much weight that it actually caused unintended health problems for him for years after.