A new study on the long-term benefits of gastric bypass surgery, the most commonly performed weight-loss surgery in the U.S., finds that the procedure results in sustained weight loss in the morbidly obese, compared with no surgery, and also helps keeps diabetes and heart disease risk at bay.

The study, published on Tuesday in an obesity-themed issue of the Journal of the American Medical Association, followed 1,156 participants aged 18 to 72 who were severely obese (body mass index, or BMI, of 35 or greater) for more six years. The researchers divided the study sample into three groups: one group of 418 people who underwent surgery, one control group of 417 participants who wanted the surgery but didn’t have it, and a second control group of 321 people who did not seek surgery.

At six years, the researchers found that those who underwent gastric bypass, also known as Roux-en-Y gastric bypass, had significant improvements in their cardiovascular health as well as sustained weight loss compared with other morbidly obese participants who did not undergo surgery: on average, patients who received surgery maintained a loss of 28% of their starting weight for six years. They were also more likely to see their diabetes go into remission: 62% of the gastric bypass group, compared with 8% and 6% in the control groups.

Those who went under the knife also saw improvements in metabolic and heart disease risk factors - they were significantly less likely to have high blood pressure or High cholesterol, for example - during the six years of follow-up. “In contrast, cardiovascular and metabolic status of severely obese control participants generally worsened during the six-year period,” the authors wrote.

“These findings are important considering the rapid increase in total numbers of bariatric surgical operations performed in the United States and worldwide, and may have significant ramifications for the projected 31 million U.S. individuals meeting criteria for bariatric surgery,” the authors concluded.

However, a separate study published on Monday in the Archives of Surgery by researchers at the Madigan Army Medical Center in Fort Lewis, Washington, found that gastric bypass surgery - considered the “gold standard” surgical treatment for obesity - may have a rival: a more complex and less commonly used operation called duodenal switch surgery.

Bariatric surgeries work in two ways: by reducing stomach size or re-routing food from the stomach directly to the intestines, so the body absorbs less of it. Both gastric bypass surgery and duodenal switch combine both methods, but duodenal switch re-routes food significantly more - bypassing most of the small intestine - resulting in less absorption, but also a riskier, more complicated operation and a higher risk of malnutrition afterward. The new study found that both surgeries were successful in leading to weight loss in the morbidly obese, but that weight re-gain may be more common with gastric bypass.

The researchers compared 1,545 patients, with an average BMI of 52, who underwent duodenal switch and 77,406 patients, with a BMI of 48, who underwent gastric bypass surgery between 2007 and 2010. (A BMI of 40 or higher is considered morbidly obese, and a BMI of 50 or higher is considered super obese.) At the two-year follow-up, participants who underwent duodenal switch had maintained a 79% loss of excess body weight, compared with a 67% loss maintained by gastric bypass patients. The researchers also found that nearly 20% of gastric bypass patients had failed to lose at least 50% of their excess weight by both the 1- and 2-year follow-ups - constituting failure of the weight loss surgery - compared with failure rates of 9% and 6% at 1 and 2 years, respectively, among the duodenal switch patients.

They found that duodenal switch patients were also more likely to have control of obesity-related conditions like diabetes, high blood pressure and sleep apnea after surgery, especially among participants who started out with a BMI greater than 50. In general, however, these patients started out in worse health: they were significantly heavier and they were more likely to have more severe obesity-related health problems, compared with gastric bypass patients.

The major downside of the duodenal switch procedure is that it’s riskier. Patients who received duodenal switch had longer surgeries and more blood loss during the operation than gastric bypass patients; they also stayed in the hospital nearly twice as long after surgery, required follow-up surgery more frequently early on, and were significantly more likely to suffer post-operative infections and leaks. They also had a higher risk of death and were much more likely to develop a nutritional deficiency. “This is the most aggressive procedure with the highest risk, but it comes with the best potential for reward,” says study author Dr. Matthew Martin.

Currently, duodenal switch is more commonly used in Europe than the U.S., but Dr. Martin thinks it will take off in America similarly to gastric bypass. “When gastric bypass surgery started out, there was a complication rate of 5% to 10% and a death rate of up to 1%, all of which have been markedly lowered as we gained experience with it. If you look at the current complications with duodenal switch, they’re about exactly what they were with gastric bypass 10 years ago. It’ a more complex procedure, which is why I think it has taken longer to become widely accepted.”

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By Alexandra Sifferlin