By Rob Stein Washington Post Staff Writer Thursday, August 23, 2007; A12

Obese people are significantly less likely to die prematurely if they undergo stomach surgery to lose weight, according to two large new studies that offer the first convincing evidence that the health gains of losing weight translate into living longer.

The research, involving about 20,000 obese people in the United States and Sweden, found that those who underwent surgery had a 30 to 40 percent lower risk of dying over the next seven to 10 years than those who went without the operations.

Previous studies showed that losing weight cuts the risk of diabetes, heart disease, cancer and other major ailments and suggested that that might lead to an increase in longevity. But the new studies offer the strongest evidence to date to answer one of the most important and contentious questions about one of the nation's biggest health problems: Does weight loss result not only in healthier lives but also in longer ones?

"The question as to whether intentional weight loss improves life span has been answered," wrote George Bray of the Pennington Biomedical Research Center in Baton Rouge in a commentary accompanying the studies in today's issue of the New England Journal of Medicine. "The answer appears to be a resounding yes."

The proportion of Americans who are overweight has been rising steadily; two-thirds are considered overweight, and a third are obese. Excess weight increases the risk of a host of health problems, but skeptics have questioned whether being fat shortens life and whether intentionally losing weight extends it.

"This is very exciting," said David R. Flum, a professor of surgery at the University of Washington. "Although we've known for years that weight loss can reduce medical conditions associated with obesity, the link between a reduction in these conditions and an increase in longevity has been elusive. This is huge."

The obese people who underwent surgery in one of the studies lost, on average, 14 to 25 percent of their body weight. The studies did not examine whether losing moderate amounts of weight, or losing weight by dieting or taking diet pills, would also translate into longer lives, but several experts said they believe it would.

"This makes it clear that if you can get people to lose weight, they are going to live longer," said Louis J. Aronne, a professor at the Weill Medical College of Cornell University. "That is what people in the field have been saying for years. Now we have proof. These papers represent a milestone."

Some experts, however, remained unconvinced. They argued that the longevity benefit in the studies was relatively small, especially when weighed against the risks of stomach surgery.

"I would hate to see these studies being used to justify the argument that we should be doing weight-loss surgery to save lives," said Paul Campos, a law professor at the University of Colorado and the author of "The Obesity Myth." "The claim that we have to give people weight-loss surgery to keep them from dying imminently is greatly exaggerated . At best it's a very, very modest effect."

In fact, the data could be interpreted as showing that obese people fare fairly well without surgery, others said. Mortality for those who were not treated remained very low, they said.

"Until today, we have had little information on how well extremely obese people do without treatment," Paul Ernsberger, a professor of nutrition at the Case Western Reserve University School of Medicine, wrote in an e-mail. "Even though the group ranged up to 60 years of age, 96 percent of them survived for 10 years. Nearly 88 percent survived for 16 years. These are far better odds than doctors are predicting for their fat patients."

But others said the studies demonstrated a clear advantage from surgery. In the first study, Ted D. Adams of the University of Utah and colleagues looked back at 7,925 severely obese people who had undergone stomach surgery and 7,925 similarly obese people who had not. After an average of about seven years, those who had stomach surgery were about 40 percent less likely to have died, the researchers found. Those who underwent surgery were 92 percent less likely to die from diabetes, 60 percent less likely to die from cancer and 56 percent less likely to succumb to heart disease.

In the second study, which several researchers said was even more convincing, Lars Sjostrom of Goteborg University in Sweden and colleagues followed 2,010 obese patients who underwent stomach surgery and a similar group of 2,037 patients who did not have the operation, known as bariatric surgery. Over the next 11 years, on average, those who had surgery were about 30 percent less likely to die from any cause.

"This study for the first time offers strong evidence that intentional weight loss, or at least bariatric surgery, is associated with decreased mortality," Sjostrom said.

Sjostrom and Adams acknowledged that they did not have enough data about different levels of weight loss to determine how much of the benefit was from losing weight and how much might have been from other effects of the surgery.

"I think it's certainly related to weight loss, but there may be other mechanisms happening that are also playing a role in addition to weight loss connected to the surgery itself," Adams said.

The findings were hailed by proponents of stomach surgery, which has been controversial. The procedures involve reducing the size of the stomach through various techniques. The number of Americans undergoing the procedures has risen quickly in recent years, and about 178,000 are now done annually. Critics have questioned whether the expensive procedures' risks, which can include life-threatening complications, outweigh the benefits for many patients, and whether they are being done too frequently.

"These are landmark studies," said Kelvin Higa, president of the American Society for Metabolic and Bariatric Surgery. "These studies clearly show that bariatric surgery saves lives."

Several other experts agreed that the studies provide strong support for the surgery for severely obese patients but questioned whether the procedures are being done too frequently on less overweight patients who might be able to lose weight through other means.

"I would argue that making fundamental changes in our lifestyles would be a healthier and, in the long run, more efficient goal," said David Zingmond of UCLA's David Geffen School of Medicine.