The two plans are among the most popular and had the best evidence that dieters could lose meaningful amounts of weight and keep it off for at least a year, the review authors said.
Pooling results from several studies, the researchers found that Weight Watchers dieters lost an average of at least 8 pounds and kept it off for at least 12 months versus about 15 pounds for those using the Jenny Craig plan.
Most participants remained overweight, with weight loss of between 3 per cent and 5 per cent of their initial weight — but that's a range that doctors typically recommend to achieve healthful benefits including lower blood pressure and cholesterol levels.
"It's a really important first step to reach," even if it doesn't meet patients' expectations, said study author Dr. Kimberly Gudzune, an internist and researcher at Johns Hopkins University's medical school.
The study was published Monday in Annals of Internal Medicine.
The research review included 39 rigorous studies involving 11 popular diet programs that include support or counselling services and involve fees for products or services. Most studies compared the programs with standard diet information or behaviouralcounselling patients get from health care providers; long-term results for Weight Watchers and Jenny Craig were mostly better than the comparisons.
The researchers didn't attempt to make head-to-head comparisons of different diet plans. They note that the Affordable Care Act makes obesity screening and counselling more accessible to many Americans, and that with two-thirds of U.S. adults overweight or obese, it's important for doctors to know which diet plans work.
Diet companies had no role in the research, Gudzune said.
Weight Watchers and Jenny Craig include behaviouralcounselling, coaching or social support — important for long-term weight-loss success, according to an Annals editorial.
Weight Watchers costs about $43 monthly, which includes costs for attending online or in-person support groups or coaching sessions. Participants can buy the company's low-calorie products or buy their own food, but each item is assigned points and dieters aim not to exceed a daily point limit.
Jenny Craig provides pre-made meals and costs about almost $600 monthly.
Michele Rouse, an administrative co-ordinator at Johns Hopkins' medical school who used to work for Gudzune, says she has lost 7 pounds since starting on Weight Watchers a month ago and has already seen a drop in her elevated blood pressure. Rouse said she didn't know much about the new study and picked Weight Watchers because she'd had success with it years ago.
It's too soon to tell if the program will help her reach her 70-pound weight loss goal, but Rouse says it's a sensible plan that's more like a lifestyle change than a harsh diet.
"You're not starving yourself," said Rouse, 49.
AP Medical Writer Lindsey Tanner can be reached at http://www.twitter.com/LindseyTanner