Study Is In: Weight Watchers Works

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When it comes to weight loss, people may be better off following the commercial diet program Weight Watchers, rather than relying on guidance from their primary care doctors.

According to a new study published in the journal Lancet, overweight and obese adults who used Weight Watchers for a year lost twice as much weight as people who got weight-loss advice from their doctors.

For the study, researchers randomly assigned 772 overweight or obese participants from Germany, Australia and Britain to either a Weight Watchers program or a plan guided by a primary care doctor. The Weight Watchers group got a free 12-month membership and access to weekly meetings; the primary care group was asked to attend monthly weight-loss sessions with their doctor at the office.

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Overall, about 87% of participants were women and the average age of the entire study group was 47. At the start of the study, the volunteers’ average body mass index (BMI) was 31; overweight is defined as having a BMI of 25 or higher, and obesity is defined as having a BMI 30 or higher.

By the end of the year, the Weight Watchers group had lost an average 11.1 lbs., more than twice the 5 lbs. lost on average by those in the primary care group. The Weight Watchers members also managed to lower their fasting insulin and their cholesterol levels more than the doctor-guided dieters.

Of course, there are a few caveats: for one thing, the people who followed the Weight Watchers program didn’t have to pay for their memberships. The diet plan can cost members nearly $500 a year in the U.S., which puts it out of reach for many. Also, the study was funded by Weight Watchers, but that’s not so unusual — all major commercial diet plans fund their own studies. And, finally, about 40% of the study’s participants dropped out before the year was up.

Still, the results were pretty impressive: people in the Weight Watchers group were three times more likely to lose at least 10% of their initial body weight, compared with the primary care group. If you count only those who stuck it out for the yearlong study, people doing Weight Watchers lost 14.6 lbs., compared with 7.2 lbs. for those following their doctors’ advice.

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[T]he authors of the new study say they were surprised by how dedicated the Weight Watchers participants were — they attended three meetings a month, on average — and by how much weight they actually lost.

“I don’t think we could have predicted that people randomly allocated to Weight Watchers by their doctor — rather than choosing to attend of their own accord, which would give a selected group of probably more motivated people — would lose significantly more weight,” says lead author Susan Jebb, Ph.D., a diet and population health researcher at the U.K. Medical Research Council, in Cambridge.

The authors and other experts chalked up the Weight Watchers group’s success to the fact that the commercial diet plan offered more frequent and consistent weight-loss support — likely boosting motivation for participants — than monthly meetings with a doctor.

“It’s not terribly surprising that a group whose whole career is basically helping people with weight management would do a better job than a primary-care group that has a lot more responsibilities on top of that,” Mayo Clinic endocrinologist Dr. Michael Jensen, who was not involved in the study, told

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Therein lies the secret to any successful weight loss plan: no matter the method, it only works if you have the motivation and the dedication to stick with it.

Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.