The discovery came about by accident more than a decade ago: Weight-loss surgery often led to dramatic improvement in the control of Type 2 diabetes, often before patients left the hospital.

Today, evidence of the connection is so solid that some doctors say surgery should be considered as a treatment for diabetes, regardless of a person's weight.

``We thought diabetes was an incurable, progressive disease,'' says Dr. Walter J. Pories, a professor of surgery at East Carolina University and a leading researcher on weight-loss surgery. ``It . . . is a major cause of amputations, renal failure and blindness. This operation takes about an hour, and two days in the hospital, and these people go off their diabetes medication. It's unbelievable.''

As many as 86 percent of obese people with Type 2 diabetes find their diabetes is gone or much easier to control within days of having weight-loss surgery, according to a meta-analysis of 19 studies published earlier this year in the American Journal of Medicine (78 percent of patients with remission of diabetes and 86.6 percent with remission or improvement).

Experts still aren't sure why obesity surgery helps resolve Type 2 diabetes or how long the effect might last. And they disagree on how big a role surgery should have in treating the illness.

GLUCOSE CONTROL

This much is clear: Patients who have weight-loss surgery begin to lose weight rapidly, which by itself improves Type 2 diabetes, allowing diabetics to more easily control their blood glucose levels. But something else appears to be occurring.

There is strong evidence that surgery -- especially gastric bypass surgery, which makes the stomach smaller and allows food to bypass part of the small intestine -- causes chemical changes in the intestine, says Dr. Jonathan Q. Purnell, director of the Bionutrition Unit at Oregon Health & Science University.

Multiple studies in humans and animals indicate that surgery triggers reductions in ghrelin, the hormone that stimulates hunger, and elevates levels of peptide YY and glucagon-like peptide-1, both of which act as appetite suppressants. Another theory is that surgery might alter the expression of genes that regulate glucose and fatty-acid metabolism.

Evidence suggests the effect on diabetes can last for an extended period or even indefinitely, particularly if people don't regain a lot of weight.

DISEASE CAN RETURN

``There is durability, but we also know that some people do get the disease back again,'' Purnell says. ``Weight rebound is probably one factor. We also know that diabetes is a progressive disease. It may depend on how long you've been diagnosed with diabetes. If it's early on, I think the durability may be better.''

It's not clear yet why people have different responses.

``There is some evidence that African-Americans don't respond as well as Caucasians, and men don't respond as well as women,'' Pories says.

Despite the unknowns, the evidence that a majority of people experience long-term improvement in blood glucose control suggests the surgery could eventually play a greater role in the treatment of obese people with Type 2 diabetes.

Medical guidelines, which insurers follow, state that weight-loss surgery should be restricted to patients with a body mass index of 35 or greater who have related health problems. Several studies are under way, or will soon begin, to examine the benefits of surgery in people with Type 2 diabetes and a lower BMI.

In the United States, weight-loss surgery is still largely viewed as a cosmetic procedure and obesity as a lifestyle issue, not a chronic disease. Moreover, weight-loss surgery carries risk. The death rate is about 1 per 200 operations, and severe complications can occur, including blood clots, infection related to surgery, and the need for corrective surgery.