A very simple description of the study:

The experiment lasted for 14 day and involved three men all of similar athletic ability and physique. During the first three days, the subjects glycogen stores were depleted to near zero; then from days 4 through 12 (9 days in all), the subjects were overfed on a high-carbohydrate, low-fat diet. Approximately 3600 extra carbohydrate calories per day were needed to produce an overfeeding condition. Subjects also exercised twice a day (30 mins each time) and they could do additional exercise, but they were not allowed to do any anything strenuous (other than the two assigned workouts).

Interestingly, the subjects in the study spontaneously burned more calories during the 9 days of over-feeding, too;
so the scientists had to keep increasing calories to maintain an over-feeding state. On average, test subjects
spontaneously burned an extra 840 calories per day, or 35% more calories, during the overfeeding period, presumably due to thermic effect (thermogenesis).Yes, you read that right: A high-carbohydrate diet causes the body tospontaneously burn more calories~up to 35% more calories than a high-fat or high-protein diet.