The changes in body weight, body fat, lean body mass, and the efficiency index were studied in a sample of 80 obese males and females undergoing four different treatments, using two treatment components: an increase in dietary fiber, and energy expenditure through exercise. In both sexes there was a significant effect of exercise upon body weight and an improvement in the efficiency index. There was also a significant interaction between fiber and exercise in girls, but not in boys. This suggests that the eventual effect of dietary fiber is heightened by exercise, as corroborated by significant differences in some of the groups.