In reviewing 46 studies with almost 12,000 people, U.S. researchers concluded that most diets result in similar weight losses. On average, the typical dieter loses 10 to 15 pounds or 6 percent of their body weight. Also, most put the weight back on after 5 years. Diets that tended to work better were those that made people consume fewer calories as well as those that included meetings with diet groups or counselors. Researchers additionally stated that weight loss drugs were similarly ineffective in the long term. It should be noted that the studies reviewed consisted of primarily government and university studies as well as Weight Watcher studies.
Source: Reuters. July 2, 2007.