TUESDAY, Jan. 3 (HealthDay News) -- Obese people who undergo weight loss surgery appear to reduce their risk of heart attack, stroke and death, Swedish researchers report.

And these heart-health benefits seem to be connected with metabolic changes that occur after the surgery, such as altered insulin production, rather than the weight loss, the researchers say.

"Bariatric surgery is associated with about 30 percent reduction both in the incidence of heart attack and stroke," said lead researcher Dr. Lars Sjostrom, a professor at the University of Gothenburg's Institute of Medicine.

"Body mass index before the operation does not predict the surgical treatment effect, while insulin concentration before surgery is strongly related to future benefit," he said.

Bariatric surgery involves altering the stomach in order to reduce the amount of food consumed or digested. Given these new findings, some experts think the criteria for the operations should include more than body mass index (BMI), a measurement that takes into account height and weight.

"Before, we thought surgery was a shortcut for patients who didn't have the willpower to lose weight on their own," said Dr. Francesco Rubino, chief of gastrointestinal metabolic surgery at Weill Cornell Medical College in New York City. However, for patients with uncontrolled diabetes or heart disease, surgery might be life-saving, he said.

"I don't think a BMI cutoff should disqualify patients," Rubino said. A BMI of 30 or more is considered obese.

The study, started in 1987 and reported in the Jan. 4 issue of the Journal of the American Medical Association, is the first prospective study to show these cardiovascular benefits from weight loss surgery, the researchers said.

Sjostrom's team, using the Swedish Obese Subjects study, looked at data on more than 2,000 study participants who underwent bariatric surgery and more than 2,000 who didn't. All were middle-aged, white and obese, with and without pre-existing health conditions.

The types of bariatric surgery included gastric bypass, in which stomach size is reduced with staples; banding, which uses an adjustable band to restrict food intake; and vertical banded gastroplasty, which also limits food intake.

During more than 14 years of follow-up, 28 people who had bariatric surgery died from a cardiovascular problem, compared with 49 who didn't have surgery, the researchers found.

There were 199 first-time heart attacks or strokes among the surgical patients, compared with 234 among the non-surgery participants, they noted.

Fewer fatal heart attacks occurred in the surgery group than the non-surgery group (22 versus 37). Surgery was also associated with fewer fatal and non-fatal strokes.

But no significant relationship was seen between weight loss and cardiovascular events in either group, the investigators found.

While that finding could be a statistical fluke, Sjostrom said other reasons could explain the finding.

"No non-surgical treatment has shown significant favorable effects on cardiovascular events in the obese," Sjostrom said.

"Our findings stress even more the favorable effects of bariatric surgery as compared to usual care. Also, all guidelines for bariatric surgery probably have to be modified since they all use BMI as the main criterion for patient selection," he said.

Dr. Edward Livingston, author of an accompanying journal editorial, agreed that weight should no longer be the determining factor for bariatric surgery.

Based on these findings, "the surgery should be targeted at treating a condition that will improve with weight loss," said Livingston, the Dr. Lee Hudson-Robert R. Penn Chair in Surgery chair of surgery at the University of Texas Southwestern Medical Center at Dallas. "There is something these patients benefit from from surgery that's not weight loss."

Obese patients who have diabetes or sleep apnea might fit this category, as well as people with knee or hip arthritis who need a joint replacement, Livingston said.

Why these conditions improve isn't clear, he noted. It could be the operation, or better medical care, or patients taking better care of themselves, he suggested.

Depending on the actual operation, bariatric surgery costs between $10,000 and $20,000 plus follow-up costs, and insurance coverage is very inconsistent, Livingston added.

"I would approach bariatric surgery cautiously. It's not a panacea. It has a lot of downsides," Livingston explained. Complications can include leaks, infections and embolism (a sudden blockage in an artery), he pointed out.

Also, many patients gain back the weight lost after the surgery. "We really don't know the very long-term results of these operations," Livingston said.

More information

For more information on bariatric surgery, visit the U.S. National Library of Medicine.