Dietician: "Recent Studies Have Shown That People Can Lose Weight

Dietician: "Recent studies have shown that people can lose weight solely by changing their diet alone, without having to increase their amount of activity. In two recent studies, overweight but otherwise healthy people cut their caloric intake and all participants lost weight without having to change their activity level, showing that weight loss through diet alone is possible."
Critic: "That is not true. While some people may have been successful, the study only covered otherwise healthy people who were likely to succeed. What about other people, who have tried to change their diets without exercising, and failed to lose weight?"
Which of the following, if true, would most undermine the dietician's argument?

A) Upon further evaluation of the study, participants divulged that they tried to exercise more than normal during the study
B) The studies were conducted with a diverse study group from various ethnic and racial backgrounds.
C) A later study evaluating whether exercise alone can cause weight loss found that changing exercise without diet can also cause weight loss.
D) A later study that included exercise and dieting found that participants lose weight the fastest when they combine diet and exercise.
E) The studies were completed by multiple researchers and peer evaluated.