CHICAGO — A new study gives the strongest evidence yet that obesity surgery can cure diabetes.

Patients who had surgery to reduce the size of their stomachs were five times more likely to see their diabetes disappear in the next two years than were patients who had standard diabetes care, according to Australian researchers.

Most of the surgery patients were able to stop taking diabetes drugs and achieve normal blood tests.

“It’s the best therapy for diabetes that we have today, and it’s very low risk,” the study’s lead author, Dr. John Dixon of Monash University Medical School in Melbourne, Australia, said.

The patients had stomach band surgery, a procedure more common in Australia than in America, where gastric bypass surgery, or stomach stapling, predominates.

Gastric bypass is even more effective against diabetes, achieving remission in a matter of days or a month, Dr. David Cummings, who wrote an accompanying editorial in the journal but was not involved in the study, said.

“We have traditionally considered diabetes to be a chronic, progressive disease,” Dr. Cummings, of the University of Washington in Seattle, said. “But these operations really do represent a realistic hope for curing most patients.”

Diabetes experts who read the study said surgery should be considered for some obese patients, but more research is needed to see how long results last and which patients benefit most. Surgery risks should be weighed against diabetes drug side effects and the long-term risks of diabetes itself, they said.

The diabetes benefits of weight-loss surgery were known, but the Australian study in today’s Journal of the American Medical Association is the first of its kind to compare diabetes in patients randomly assigned to surgery or standard care. Scientists consider randomized studies to yield the highest-quality evidence.

The study involved 55 patients, so experts will be looking for results of larger experiments under way.

“Few studies really qualify as being a landmark study. This one is,” said Dr. Philip Schauer, who was not involved in the Australian research but leads a Cleveland Clinic study that is recruiting 150 obese people with diabetes to compare two types of surgery and standard medical care. “This opens an entirely new way of thinking about diabetes.”

Obesity is a major risk factor for diabetes, and researchers are furiously pursuing reasons for the link as rates for both climb. What’s known is that excess fat can cause the body’s normal response to insulin to go haywire. Researchers are investigating insulin-regulating hormones released by fat and the role of fatty acids in the blood.

In the Australian study, all the patients were obese and had been diagnosed with type 2 diabetes during the past two years. Their average age was 47. Half the patients underwent a type of surgery called laparoscopic gastric banding, where an adjustable silicone cuff is installed around the upper stomach, limiting how much a person can eat.

Both groups lost weight over two years; the surgery patients lost 46 pounds on average, while the standard-care patients lost an average of three pounds.

Blood tests showed diabetes remission in 22 of the 29 surgery patients after two years. In the standard-care group, only four of the 26 patients achieved that goal. The patients who lost the most weight were the most likely to eliminate their diabetes.

Both patient groups learned about low-fat, high-fiber diets and were encouraged to exercise. Both groups could meet with a health professional every six weeks for two years.

The death rate for stomach band surgery, which can cost from $17,000 to $20,000, is about 1 in 1,000. There were only minor complications in the study. Stomach stapling has a 2% death rate and costs from $20,000 to $30,000.

In America, surgeons perform more than 100,000 obesity surgeries each year.

The American Diabetes Association is interested in the findings. The group revises its recommendations each fall, taking new research into account.

“There is a growing body of evidence that bariatric surgery is an effective tool for managing diabetes,” the association’s president for medicine and science, Dr. John Buse of the University of North Carolina School of Medicine in Chapel Hill, said.

“It’s just a question of how effective is it, for what spectrum of patients, over what period of time and at what cost? Not all those questions have been answered yet.”

Medical devices used in the study were provided by the manufacturers, but the companies had no say over the study’s design or its findings, Mr. Dixon said.