Many people worry about regaining weight after getting gastric bypass surgery, a weight-loss procedure for very obese patients, but a new study suggests that most patients remain lighter 10 years later.

Looking at patients four years and 10 years after weight-loss surgery, and comparing them to obese peers who didn't have surgery, researchers found that most surgery patients lost significant amounts of body weight and kept it off.

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People undergoing Roux-en-Y gastric bypass (RYGB) had the best weight loss results, losing 21 percent more than people who didn't have surgery, and 10 percent to 17 percent more than those who had weight-loss procedures known as sleeve gastrectomy and gastric banding.

Lead author Matthew Maciejewski of Durham Veterans Affairs Medical Center in North Carolina noted that this study is the first to compare weight loss among surgery and non-surgery patients over the long term.

"Our clinical colleagues have been pleasantly surprised that patients were able to maintain most of their weight loss out to 10 years," Maciejewski told Reuters Health by email.

The study team used data on 1,787 male, mostly middle aged, severely obese veterans who underwent gastric bypass surgery between 2000 and 2011 and compared their weight loss with 5,305 similarly obese veterans who did not receive surgery.

The researchers also compared weight changes after four years among patients who had gastric bypass - which shrinks the stomach and bypasses part of the small intestine, so less food is digested - and others who had different weight loss surgeries. These included 379 veterans who got gastric sleeve surgery, which shrinks the size of the stomach by three quarters, and 246 patients who got an adjustable gastric band, also known as a lap band, which constricts the stomach to limit food intake.

One year after gastric bypass surgery, patients lost 31 percent of their baseline weight while the non-surgical comparison group only lost 1 percent of their body weight.

After 10 years, the gastric bypass group maintained most of the weight loss, keeping off nearly 29 percent of their original weight, which was an average loss of 41.3 kilograms (91 pounds). By comparison, the nonsurgical patients lost 7 percent of their baseline weight, or an average of less than 6.3 kg (14 lb).

Only 3.4 percent of bypass patients regained the weight they had lost 10 years after surgery. Almost 40 percent maintained a weight loss of 30 percent or greater.

In the comparison to people who had other procedures, gastric bypass patients lost 28 percent of their body weight at the four-year mark while gastric sleeve patients lost 18 percent and lap-band patients lost less than 11 percent of their baseline weight.

The researchers note that the gastric sleeve is a simpler surgery than gastric bypass and has recently grown in popularity, though this study suggests that it may not be as effective.

When a person loses weight through dieting, the body begins to burn fewer calories, noted Dr. Jon Gould, chief of general surgery at the Medical College of Wisconsin, who published a comment on the study in JAMA Surgery. "This means that in order to maintain weight loss, a person who has been on a diet will have to eat fewer calories than someone who naturally weighs the same."

Weight loss surgery actually changes the hormones in the digestive system and causes the brain to feel less hungry and more full, leading to more sustainable long-term weight loss, he told Reuters Health.

Even people who regain weight after surgery may have better health outcomes, however, Gould said. "Weight loss is just one of the important outcomes following bariatric surgery. Improved health and quality of life are also important," he said by email.

"This study suggests that the vast majority of patients interested in bariatric surgery, especially gastric bypass, should be able to lose a significant amount of weight with gastric bypass and keep that weight off for a very long time," Maciejewski said.