In an experiment inspired by the movie Supersize Me, in which filmmaker Morgan Spurlock lived on McDonald's meals for a month, the researchers asked 12 men and six women to participate in a similar experiment.
The 18 participants -- all in their 20s, lean and in good health -- spent a month eating two meals a day at fast-food restaurants while living a sedentary lifestyle. The participants were told not to exceed 5,000 steps per day, with the goal of increasing their body weight by 5% to 15%. All but one of the participants reached that goal, while five boosted their body weight by the maximum of 15%.