MINNEAPOLIS - People who undergo weight-loss surgery don't reduce their costs as they take off pounds, as hospital stays for complications from the procedure exceed savings from obesity-related illnesses, a study found.

Researchers tracked insurance claims of 29,820 patients for as many as six years after bariatric surgery, comparing their costs with a group of people with obesity-related conditions who didn't have the procedures. While pharmacy expenses and office visits were lower for surgical patients, repeat procedures were higher, according to the study in the journal JAMA-Surgery.

Bariatric surgery is one of the most effective weight-loss methods, with studies showing the procedure yields benefits such as reduced diabetes risk and lower cholesterol for at least six years. There's no evidence, though, that it prolongs life.

The study released Wednesday shows the improvements that stem from avoiding diabetes and heart disease don't necessarily bolster health.

"This suggests that rampant bariatric surgery isn't going to be an answer to health-care costs," said Jonathan Weiner, professor of health policy and management at Johns Hopkins Bloomberg School of Public Health, and the study's lead author. "That doesn't mean that some people, some of the time won't benefit from surgery."

The study found no reduction in expenses to help recoup the $28,000 average cost of the initial surgery, with repeat inpatient hospital costs peaking after two to three years. The patients traded off the type of care they needed, with costs remaining stable at roughly $9,000 a year.

The number of procedures performed in the U.S. topped 220,000 in 2009, according to the American Society for Metabolic & Bariatric Surgery. The procedures, which achieve weight loss by restricting the size of the stomach, include gastric banding that is adjustable and reversible, and gastric bypass, in which part of the stomach is closed and the other is connected to the small intestine.

"Future studies should focus on the potential benefit of improved health and well-being of patients undergoing the procedure rather than on cost savings," Weiner said in a statement.

Allergan Inc., which sells the Lap-Band weight loss device, said Feb. 5 it will sell its obesity-treatment unit in the first half of 2013. The unit's sales tumbled 22 percent in the fourth quarter to $36.8 million. Annual sales are down from a peak of $296 million in 2009 amid questions about the stomach-shrinking device's risk and lawsuits stemming from surgical complications.

More than 500 million people worldwide are obese, according to the World Health Organization. In the U.S., more than 44 percent of adults may be obese by 2030, according to a report from the Trust for America's Health and Robert Wood Johnson Foundation. Obesity-related health costs in the U.S. now top $168 billion annually, the researchers said.

"Coupled with findings that bariatric surgery confers little to no long-term survival benefit, these observations show that bariatric surgery does not provide an overall societal benefit," Edward Livingston, JAMA's deputy managing editor, wrote in an editorial accompanying the study. "In this era of tight finances and inevitable rationing of health-care resources, bariatric surgery should be viewed as an expensive resource that can help some patients."

The surgery should only be offered to those who have clear health problems tied to obesity, such as diabetes or arthritis, he said.