By Shereen Lehman

(Reuters Health) – Obese patients who have weight loss surgery often see their diabetes improve, but whether the surgery helps prevent diabetes in the first place hasn’t been clear.

A new study suggests that weight loss surgery does help prevent diabetes, but experts say the data still don’t allow for a definite answer.

In the study, obese patients who underwent so-called bariatric surgery were less likely to develop type 2, or “adult onset” diabetes compared to similar patients who did not have the surgery.

Martin Gulliford at King's College in London and colleagues used electronic health records from the U.K. Clinical Practice Research Datalink to compare 2,167 obese adults without diabetes who had the weight-loss surgery and another 2,167 people matched for age, sex, body mass index, and blood glucose control who did not have surgery or other obesity treatments.

Patients in the surgery group had one of three procedures -- laparoscopic banding, gastric bypass, or sleeve gastrectomy, the researchers reported in The Lancet Diabetes & Endocrinology.

The participants were followed for an average of about three years. During that time, 38 people who had weight loss surgery developed diabetes, compared with 177 people in the control group.

That translated to an 80 percent lower risk of developing diabetes for the surgery patients, even after the researchers took smoking habits, high blood pressure, and high cholesterol into consideration.

“This study, together with earlier results from a study in Sweden, shows that weight loss surgery in people with severe obesity is associated with a substantial reduction in the risk of type 2 diabetes,” Gulliford said.

He added, “The study adds to increasing evidence that weight loss surgery may be effective at reducing the adverse health impacts of severe obesity.”

But in a commentary published with the study report, Dr. Jacques Himpens cautions while the results bring us closer to confirming the effect of weight loss surgery on the risk for developing type 2 diabetes, “many questions still remain unanswered, and more evidence is needed to convince endocrinologists about the nature of this effect.”

Himpens, from the Saint Pierre University Hospital in Brussels, Belgium, says the conclusions make sense but he fears the researchers compared two groups that were not really comparable.

“One group was not being treated – they were just being watched without any medication or any lifestyle changes or anything and they were compared to the people that had the most active treatment which is surgery so I don’t think that’s fair – the two groups aren’t comparable,” he told Reuters Health.

Himpens is also concerned about the short length of time because weight loss surgery patients often regain weight many years later.

“I am sure that had the authors conducted the study for more than six, seven, or eight years, the numbers would have been far worse than what they had now,” he said.

“I think we have to be very careful that what we do is actually good for the people because we really have to make sure that we can follow up with those patients,” Himpens said.

He said that he often sees patients who skipped their follow up care after their procedures, but return nine or ten years later, “and they’re miserable because they neglected their diet, they didn’t exercise at all and we see they experience weight re-gain, they suffer from all kinds of diseases including diabetes.”

But he added that patients who see their doctors regularly usually do very well.

“They keep their weight down, they do not develop diabetes or other co-morbidities,” Himpens said. “So I think the message is that it’s great to do bariatric surgery, but we need to make sure that (patients) do commit themselves to come back for follow up and make sure that they will really stay under medical guidance.”

SOURCES: and The Lancet Diabetes & Endocrinology, online November 3, 2014.