Changes in body weight, nitrogen, water, and total body fat were evaluated, with two independent techniques, in four obese patients during seven consecutive 16-day periods during which each patient was starved for 16 days and then fed an 800-calorie liquid diet for 16 days before again being fasted. The major component of the body weight loss during every starvation period was not fat, but water and protein. The periods of caloric restriction which followed each starvation period were characterized by minimal change in body weight and rapid reaccumulation of water and nitrogen. Fat loss, although variable in magnitude, was constant throughout starvation and caloric restriction. The average cumulative fat loss during 48 days of total starvation was not significantly different from the average fat loss during 48 days of caloric restriction.