The number of weight-loss foods and programs can be overwhelming. But only a select few have evidence that shows they work.

Patients who are in the market for a weight-loss program should go with Weight Watchers or Jenny Craig, according to a paper published today in the Annals of Internal Medicine.

The paper looked for valid studies supporting the claims of commercial weight-loss programs and products, including Atkins, Slimfast, Nutrisystem, and The Biggest Loser Club. Researchers said most programs lacked evidence showing they work and are safe. They identified 32 diet programs to study, but were able to locate scientific studies of only 11 of them, and most studies lasted for less than one year.

Only Weight Watchers and Jenny Craig can point to studies showing long-term results and safety, the report concluded.

The analysis updates a 2005 Annals of Internal Medicine exploration of the same topic. That report determined only Weight Watchers had evidence supporting its program.

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More than one third of U.S. adults are obese. Healthcare costs associated with obesity were estimated at $147 billion in 2008, according to an editorial that accompanies the study.

“Unfortunately, far more resources are spent on managing obesity’s complications than on treating the condition itself,” Dr. Christina Wee, MPH, of the Beth Israel Deaconess Medical Center and Harvard Medical School, wrote in the editorial.

Doctors often can’t or don’t guide their patients through weight-loss programs themselves, which has caused commercial programs and products to become increasingly important.

“Obesity for the longest time hasn’t been under the medical umbrella. It’s really in the last couple years that it’s been recognized as a chronic condition,” Dr. Kimberly Gudzune, an author of the paper and an assistant professor of medicine at Johns Hopkins University, told Healthline. “Because of that, more weight loss is in the commercial space.”

The authors hope their study of weight-loss programs will make doctors more confident in helping patients who are trying to get slimmer.

“Most people don’t think about talking to doctor about ‘I want to lose weight,’ and I’m hoping that more of those conversations come within the medical setting. I hope this study will give physicians the tools to start helping folks,” Gudzune said.

Patients may also get increased coverage for weight loss.

The Affordable Care Act mandates full coverage of preventative medicine. It specifically includes obesity screenings and dietary counseling with a doctor.

Insurance companies may eventually offer coverage for weight-loss programs.

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Doctors can feel comfortable referring patients to either Jenny Craig or Weight Watchers, the study concludes. But even those two research-driven programs are not alike.

The Jenny Craig program resulted in more weight loss than Weight Watchers. But Jenny Craig, which includes prepackaged meals along with behavioral counseling, cost significantly more. Jenny Craig membership runs $500 a month, while Weight Watchers costs $40.

Weight Watchers, the only company that responded to a request for comment before Healthline’s publication deadline, sees its reliance on real food not just as cheaper but also as more likely to bring long-term results.

“For the end user to be able to choose the foods they want to eat at home, in restaurants, in the work place — or anywhere else food shows up in our lives — Weight Watchers delivers a livability and long-term sustainability that’s compelling,” said Gary Foster, Ph.D., chief scientific officer of Weight Watchers International, Inc.

The researchers note that Nutrisystem also showed promising results for short-term weight loss but lacked evidence for longer-term success.

Short-term findings also suggest that low-calorie meal replacements such as Optifast are an effective weight-loss strategy, but the study points to the lack of year-long studies and the possible risks. Rapid weight loss can overtax the gallbladder, which flushes cholesterol from the body, Gudzune explained.

Atkins diets, Slimfast, and popular online weight-loss groups didn’t result in significant weight loss, according to the study.

As for more nuanced questions of health, the study authors plan next to analyze the effects each of the diets had on blood pressure and blood sugar, Gudzune said.

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