Dr. David Ludwig from Harvard randomly divided two groups of overweight adolescents.18 One group was given water and diet drinks to consume while the control group continued with their usual drinks. At the end of two years, the diet soda group was consuming far less sugar than the control group. That’s good—but that is not our question. Does drinking diet soda make any difference to adolescent obesity? The short answer is no. There was no significant weight difference between the two groups.