Filmmaker Morgan Spurlock embarks on a journey to find out if fast food is making Americans fat. For 30 days he can't eat or drink anything that isn't on McDonald's menu; he must eat three square meals a day, he must eat everything on the menu at least once and supersize his meal if asked. He treks across the country interviewing a host of experts on fast food and a number of regular folk while downing McDonald's to try to find out why 37% of American are now overweight. Spurlock's grueling diet spirals him into a metamorphosis that will make you think twice about picking up another Big Mac.