Hall quickly learned that in reality-TV-land, a week doesn’t always translate into a precise seven days, but no matter: the weight being lost was real, speedy and huge. Over the course of the season, the contestants lost an average of 127 lb. each and about 64% of their body fat. If his study could uncover what was happening in their bodies on a physiological level, he thought, maybe he’d be able to help the staggering 71% of American adults who are overweight.