An analysis of 4,200 commercial weight loss programme studies failed to provide researchers at the Johns Hopkins University School of Medicine with concrete evidence of their effectiveness. This suggests health and wellness businesses have a prime opportunity to offer diet and exercise programmes targeted at weight loss, provided they can back up the proposition with 12-month-long evidential studies.

Published in the Annals of Internal Medicine, the researchers collected peer-reviewed research articles from major research databases and the weight-loss programmes themselves. Focusing on studies that lasted 12 weeks or longer and on randomised controlled tests, the scientists used results from 39 trials covering 11 programmes.

Weight Watchers, Jenny Craig and NutriSystem were three high-intensity programmes chosen for the study – each of which incorporates goal-setting, self-monitoring, nutritional information and counselling. Three very-low-calorie meal replacement programmes were also included, such as HMR, Medifast and Optifast. Five self-directed programmes were used: Atkins; Slimfast; and the internet-based Biggest Loser Club; eDiets and Lose It!

Based on their analysis of the studies, the researchers found Jenny Craig and Weight Watchers were backed by effective clinical trials that lasted 12 months or longer and showed programme participants achieved a greater weight loss than non-participants. NutriSystem also produced more weight loss at three months than counselling or education alone, but the study’s authors were unable to find any long-term trials of that programme.

Participants in the very-low-calorie meal replacement programs lost more weight than non-participants in trials lasting from four to six months. But the authors found only one long-term study, which showed no benefit from such a programme at 12 months. The authors noted that very-low-calorie programmes also carry higher risks of complications, such as gallstones.

Programmes based on the Atkins diet – high in fat, low in carbohydrates – also helped people lose more weight at six months and 12 months than counselling alone. In contrast, no definite conclusions could be made about Slim-Fast and Internet-based programmes.

"We want people to experience the health benefits of weight loss – lower blood pressure, cholesterol and blood sugar, and lower risk of developing diseases like diabetes," said Jeanne Clark, director of the division of internal medicine and study co-author. "Those benefits are long-term goals, because losing weight for three months, then regaining it, has limited health benefits. That's why it's important to have studies that look at weight loss at 12 months and beyond."