Dr. Pieter A. Cohen, a primary-care doctor at the Cambridge Health Alliance in Massachusetts and an assistant professor at Harvard Medical School, said several of his patients had used such clinics, only to return to him in frustration. “My clinical experience is that at least nine out of 10 patients who do these kinds of diets don’t just regain the weight, but go up again,” he said.

Few clinics follow patients long enough to demonstrate their programs’ effectiveness, although they point to individual success stories and say they do offer comprehensive behavioral counseling. Some are trying to improve treatment standards by employing doctors with backgrounds in obesity and certified nutritionists, while recommending only evidence-based treatments. And they say they offer real options to patients who have been shunned by mainstream medical providers.

“Doctors — even my own doctor — they would just say, ‘Stay under X calories and get lots of sleep and get lots of water,’ ” said Cris Cawley, chief executive of Thinique, a small medical weight-loss chain based in Texas. “But that’s really difficult.”

But often the clinics are overseen by doctors who have left other practices they found unprofitable. In many cases, the physician oversight amounts to little more than reading patients’ charts from afar, while the real weight-loss counseling is left to assistants with little training in the field.

One recent job posting for a medical director of a Medi-Weightloss clinic in Connecticut described the position’s hours as “not very demanding” and said the doctor would mainly be reviewing patient records remotely.

“This may be the opportunity you have been looking for,” the posting said. “There are no set hours and you will have no emergency calls.”

Dr. Edward Zbella, the chief medical officer at Medi-Weightloss, which has 76 locations around the country, said the requirements for clinic medical directors vary greatly from state to state, and in some places — like Connecticut — they supervise the work of nurse practitioners or physician assistants, who are the ones seeing patients.