This is the time of year when many people vow, once again, to lose some weight. With so many diet plans out there, it is no wonder people are confused about which plan to follow. To further confuse the hapless dieters, a study published today indicates that none of the top ten commercial weight-loss programs are all that effective in helping people lose weight and keep it off.

Dr. Thomas Wadden, who is the director of the weight and eating disorders program at the University of Pennsylvania is the lead author of the new study published today in the Annals of Internal Medicine. His conclusion is that, other than Weight Watchers, none of the other commercial programs have been able to show evidence that their programs are effective. Even Weight Watchers' participants only showed a weight loss of 5 percent three to six months after starting the program.

While weight loss companies inundate the airways and print media with ads claiming that their programs ensure results, there have been no carefully controlled studies to prove their plans work. Dr. Wadden set out to either prove or disprove their claims. He tried to find research from the companies that would support their claims of success. His group was only able to find ten such studies that lasted at least twelve weeks and then evaluated the participants a year later.

The 2003 Weight Watchers study, which was published in The Journal of the American Medical Association in 2003, evaluated 423 people all of whom weighed 205 pounds or more. Half the people were encouraged to go to WW meetings, while the other half dieted on their own. Of those who followed the Weight Watchers' program for two years, the average weight loss was 6.4 percent, while those who did not participate lost no weight.

There were no evaluations of Jenny Craig or L.A. Weight Loss available. The research group reviewed data from programs that involve low calorie diets such as Optifast, Health Management Resources and Medifast. While these companies advertise that participants can lose 15 to 25 percent of their body weight in six months, researchers were unable to find any controlled studies to back up this claim.

Naturally, executives from the companies in question were quick to respond, saying that their customers’ testimonies would confirm the companies' claims of success.