Stomach-stapling surgery to combat obesity may be done in the future with a tube inserted through the mouth, making the procedure safer than using an incision, and opening the way for more people to undergo it, doctors say.

Doctors have performed about 1 million bariatric surgeries worldwide, in which the stomach is stapled to make it smaller so people eat less, and experts say it's the best method to lose weight and keep it off.

Doing the surgery without incisions will make it a lower-risk, lower-cost proposition and may be applicable to patients who are less obese than those who are currently considered for surgery, said Dr. Philip Schauer, head of bariatric surgery at the Cleveland Clinic, which is hosting a three-day meeting on obesity.

The advent of laparoscopic surgery, also known as "keyhole" surgery, revolutionised all surgical procedures. It boosted demand for bariatric surgery in particular in the 1990s because it requires only a few small incisions, improving recovery time.

"I believe we are perhaps on the verge of another revolution," said Schauer, who was recently named president of the American Society of Bariatric Surgery.

Natural orifice transendoscopic surgery, or NOTE, requires no incisions because instruments - like long tubes with robotic arms and staple guns - can be inserted through the mouth and snaked down the esophagus.

Another possibility, he said, is inserting a sleeve, or a tube, into the intestines that would interfere with calorie absorption.

Those are about five to 10 years away, he said.

If the work to be done involves the lower portion of the intestines, instruments can be inserted through the rectum, he added.

Using a natural orifice, like the mouth or the rectum, Schauer said, would drive down costs even more because the procedure could be done without anesthesia, which would also make it less risky.

"Gaining access to the organ you want to work on is half the trauma," he said. "If there's less risk, maybe we could do (bariatric surgery) on patients with a lower BMI, maybe under 35, as a preventive operation."

Obesity is usually gauged by a body mass index, or BMI, which uses weight and height to calculate body fat. A six-foot-tall adult would be classified as obese at 222 pounds, for example. About one-third of US adults are classified as obese.

Experts say most innovation in medical technology is emerging from small privately held companies that usually get purchased by the big makers of surgical instruments, like Johnson & Johnson or Tyco Healthcare.

Dean Geraci, director of market development for auto suture bariatrics at Tyco, said it takes years to design these products and get them approved.

Engineers have to work with surgeons to determine techniques and then the devices have to go through the regulatory process, which can also be lengthy.

Venture capitalist Dr. Lee Wrubel, a general partner at Foundation Medical Partners, said an investor must have a 10-year horizon.