The Minnesota Starvation Study

During the second world war, a radical experiment was undertaken to determine the effects of starvation on the human body and mind. All the subjects were volunteers, conscientious objectors who had made themselves available for scientific experiments in lieu of combat service. It was stressed that there was no guarantee this would not cause permanent damage. The starvation treatment had terrible physical and mental effects (from premature aging to a tendency to self-mutilate), but it taught science a lot of valuable information about starvation, which was very relevant to war-torn countries where food was scarce. (The calorie restriction, by the way, was less severe than that recommended by many weight loss diets today.)

Fascinating stuff on this and other food- and body-weight-related research at Junkfood Science.