So what did they find in those 17 studies? Of the 3030 dieters Ayyad and Andersen reviewed, 30 percent dropped out. Of those who remained, 15 percent were defined as "successful dieters," those who either kept all of their weight off or maintained a weight loss of at least 20 to 24 pounds for three years or more. They also found that dieters who participated in group therapy or maintained contact with their diet clinic were twice as successful as those who did not.

Successful weight loss requires a permanent lifestyle change including physical activity.

Perhaps one of the most notable features of this review, however, is that the Danish researchers had a difficult time even finding reliable studies on the topic. Of the 900 studies published on obesity and dieting in the last 30 years, they felt that less than 2 percent of them were worthy of review. "If our criteria for inclusion had been more rigorous, very little information might well have been gathered," Ayyad and Andersen said, "and if our criteria had been weakened, too much dubious information would have disturbed the conclusions."

Average Science

	"Losing weight may be easy; however, maintaining the weight is much more difficult -- but not impossible."

An American group looked at the question of long-term weight loss success in a different way. Rather than talking about how many people succeeded or failed at keeping off the weight, they came up with an average total weight loss at the end of five years. The researchers looked at 29 studies of structured weight-loss programs and found that on average obese dieters kept off about six pounds by the end of five years. That's almost a quarter of the average initial weight loss. And as the authors remark, the dieters may well have gained weight over the years if they hadn't participated in the weight-loss programs at all, since control subjects in one study gained about 14 pounds over 5 years of normal life.

Which dieters had the most success? People who initially lost more than 44 pounds did better at keeping weight off in the long term than those who lost less than 20 pounds. And those who stuck to a very-low-calorie diet of meal replacements during the weight loss phase fared better in the long term than those who ate reduced amounts of regular food. People who exercised were more successful in maintaining their weight loss as well. Men and women fared about the same.

According to researchers who studied 29 structured weight-loss programs, people who used low-calorie meal replacements were more successful in maintaining weight loss in the long term.

The problem with a meta-analysis like this one is that the authors can't really design their own study so their conclusions are only as good as the data they find published in previous articles. Unfortunately, the quality of that data is not very good. Most studies had people who dropped out by the time five years rolled around so no one knows how much weight they kept off or, more likely, put back on. Lots of studies relied on self-reported weight. Not all the studies addressed the same variables. As the authors themselves point out, "The true effect of a weight-loss intervention could be best assessed in a long-term randomized controlled clinical trial." To date, such a study has not been
done.
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Photos: Robert Wood Johnson Foundation