NEW YORK CITY—More than 30 million of the Americans classified as obese or extremely obese might benefit from surgery that reconstructs the stomach to accommodate less food. A new study shows that gastric bypass surgery, which leads to weight loss and improvement of related health problems, may yield long-term health benefits. Earlier research had shown improvements but most patients were tracked for shorter intervals.

A report published online September 18 in JAMA, Journal of the American Medical Association tracked hundreds of extremely obese patients for six years (body mass index (BMI) above 40 or greater than 35 with health complications) and found that even after this lengthy period of time, those who received the surgery had significantly better health outcomes than those who did not. Preexisting type-2 diabetes went into remission more than half of the time (62 percent of cases).

Researchers were unsure if gastric bypass, in which the stomach is reattached farther down on the digestive tract allowing for less food absorption would lead to better long-term health without other interventions, such as dietary or exercise assistance.

For the study, the researchers enrolled 835 extremely obese patients who were seeking a from of gastric bypass known as Roux-en-Y. About half of those patients ended up getting the procedure. As an additional control group, the researchers enrolled 321 extremely obese people from the community who were not trying to get the surgery.

Following up with the participants two years later, the researchers found dramatic results. Those who had the surgery experienced a roughly 35 percent weight reduction—for many as much as 100 pounds or more under their baseline weight—whereas the control groups remained extremely obese. Even after six years and without other interventions, the patients who had the surgery were still about 28 percent lighter on average than before and experienced improved quality of life scores compared to the control groups.

Stunningly, the procedure lead to at least an 80 percent reduction in the risk of developing type-2 diabetes and a 20-times larger chance that existing diabetes would go into remission. It also lowered risks for cardiovascular disease and hypertension. Those without surgery had increased risk for all of these conditions after six years.

Other lifestyle changes recommended by health professionals in the course of receiving the gastric bypass procedure might have helped patients make more healthful lifestyle choices than those in the control groups. But, as Adams noted at the briefing, even intensive lifestyle interventions usually shave off less than 10 percent of a patient's total weight—and keep off only around 2 percent four years later.

The procedure is not, of course, a panacea. It carries risk of complications, as any major surgical procedure does. And with such an extreme loss of overall weight, patients often also experience loss of muscle mass, Ted Adams, of the University of Utah School of Medicine and Intermoutnain Healthcare in Salt Lake City, the lead researcher on the study, explained at a press briefing Tuesday morning in New York City. Researchers are now investigating the best ways to incorporate strength training into post-procedure regimes for patients.

This study and others with even more patients have also found a higher rate of suicides and a higher frequency of "poisonings of indeterminate intent" in those who have had gastric bypass surgeries compared with similarly obese counterparts. He pointed out that while the rates are still relatively low, these patterns warrant further study. Many chemicals, from alcohol to medication, are metabolized differently once the gut has been drastically remodeled. And those changes could affect mental states as well as reactions to drugs. For some, Adams suggested, they might have unrealistic expectations for how drastically their lives will change after the procedure and find improvements to be lacking.

The findings, on the whole, are encouraging, especially as extreme obesity is rising more rapidly than for the obese with lower BMIs, measuring 30 to 39.9. Extreme obesity, for example, would include a woman who is 5 feet, 6 inches and weighs 250 pounds (her BMI would be just over 40) as well as a man who is 5 feet, 11 inches tall and weighs 290 (his BMI would also be just above 40).

Adams and his team are continuing the study and hope to have results from the 10-year follow-up in a few years to see if health benefits continue. And with the striking rate with which type-2 diabetes went into remission for years after the procedure, Adams noted, researchers are now investigating whether bariatric surgery, itself, could be used as a treatment for diabetes even for people who are not currently eligible for the procedure based on their BMI alone.