Prior studies have found stomach stapling and other obesity surgeries improved survival rates after two to 10 years. The new study in mostly older male veterans suggests one of two things: Not everyone gains equally from surgery, or a survival benefit may show up later in older men, after more years of follow-up.

Previous findings came mainly from studies of mostly younger women.

“Nearly all prior studies have found bariatric surgery to be associated with reduced mortality. But those studies were conducted on very different patient populations using less rigorous methods,” said lead author Matthew Maciejewski of the Veterans Affairs Medical Center in Durham, N.C.

The patients’ organ damage from obesity could have been too far along for weight loss surgery to reverse it, some experts said.

“It may be too little too late,” said Dr. Philip Schauer of Cleveland Clinic’s Bariatric and Metabolic Institute. He was not involved in the study. “You may have to intervene earlier for a survival benefit.”

Evidence has been mounting for the health benefits of obesity surgery, so the new results may surprise some people. U.S. doctors now perform more than 200,000 obesity surgeries a year at an estimated cost of $3 billion to $5 billion. Schauer said a definitive study on survival could cost $200 million.

The new study, released Sunday to coincide with a medical meeting, will appear in Wednesday’s Journal of the American Medical Association.

Benefits of obesity surgery — improved quality of life, weight loss and reductions in diabetes symptoms, blood pressure and sleep apnea — may be reason enough to choose the treatment.

“These results are not an indictment of surgery,” Maciejewski said. He and his colleagues plan to follow the patients longer to see if a survival benefit shows up 10 to 14 years after surgery.

The study, while rigorous, wasn’t the gold standard where people are randomly assigned to have one treatment or another. Instead, researchers compared nearly 850 patients who had surgery in Veterans Affairs hospitals with other obese veterans. The two groups were as similar as possible, matched for age, gender, race and marital status.

After nearly seven years, the two groups were equally likely to be alive.

Without the painstaking matching analysis, the researchers did see a lower death rate in the surgery group compared to a group of obese patients who didn’t have surgery. But that could mean the patients who underwent surgery were healthier than the patients who didn’t.

All the surgery patients had gastric bypass, a method that makes the stomach smaller by stapling and allows food to skip much of the small intestine. The smaller stomach holds less food and the digestive detour means the body absorbs fewer calories.

The patients had surgery between 2000 and 2006. Their average age was 49 and their average body mass index was 47. A BMI of 30 or more is considered obese.

In the study, 11 patients died within the first month after surgery, a rate four times higher than in other studies. That could be because the surgery is more difficult in men than in women, said study co-author Dr. Edward Livington of University of Texas Southwestern School of Medicine.

“Women tend to collect fat in the thighs and hips rather than in the abdomen,” Livingston said. Men’s fat accumulates in the belly, making it trickier for surgeons to get through it to the organs.

Some outside experts were troubled by the post-surgery death rate. Dr. David Flum of the University of Washington School of Medicine said, regardless of the cause, the higher death rate after surgery would make it difficult to demonstrate a survival advantage.

Dr. Bruce Wolfe, president of the American Society for Metabolic & Bariatric Surgery and a professor of surgery at Oregon Health & Science University in Portland, said the researchers may see a survival benefit with more years of follow up.

“This probably won’t deter many people who want surgery,” said Wolfe, who wasn’t involved in the new study. “They’re sick. They have joint disease. They have trouble breathing. They’re doing it to improve their health and quality of life.”

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Carla K. Johnson can be reached at http://www.twitter.com/CarlaKJohnson.