Many popular diets exist, each with a different "eating plan" designed to promote weight loss. Common diets include the Atkins diet, Weight Watchers, the Zone diet, and the Ornish diet. Although these diets can be effective, there does not appear to be an advantage to any particular diet. In addition, many individuals do not lose weight when following these diets. What could be a reason that weight loss does not occur when someone follows one of these fad diets?