For people with obesity, a procedure rarely performed in the US more effectively eliminates type 2 diabetes than Roux-en-Y gastric bypass, a small study shows.
Researchers thought that the less common procedure—called biliopancreatic diversion—better reduces diabetes because it typically causes greater weight loss than the more common surgery. But in a small study, the researchers found that biliopancreatic diversion appears more effective at eliminating diabetes not just because of greater weight loss but also because the procedure itself seems to make patients more sensitive to insulin.
“Our results help explain the high rate of diabetes remission in patients who have biliopancreatic diversion surgery,” says senior author Samuel Klein, professor of medicine and nutritional science at Washington University in St. Louis. “These data suggest that we should take a closer look to see whether it might be a better option for some bariatric surgery patients.”
For the study, published in Cell Metabolism, researchers compared the effects of the two surgeries on insulin and glucose sensitivity in patients who, after their operations, lost 20% of their body weight.
Insulin is the hormone that helps the body keep blood sugar under control. Being more sensitive to insulin allows cells in the body to use glucose in the blood more effectively and helps lower blood sugar.
How do the two procedures differ?
Roux-en-Y gastric bypass surgery makes a patient’s stomach smaller by sewing parts of the stomach together to create a pouch about the size of an egg. Surgeons then connect that pouch to the upper section of the small intestine, bypassing a small portion of the upper intestine.
Biliopancreatic diversion is a more complicated surgery. Past studies have found that patients who have the surgery tend to have more postoperative complications.
In this procedure, the surgeon removes the lower part of the stomach, and connects the upper part of the stomach to the end of the small intestine, close to where it empties into the large intestine. Because the procedure bypasses so much of the intestine, the intestine absorbs fewer nutrients from food, putting patients at a higher risk for long-term nutritional deficiencies. So doctors need to closely monitor patients to make sure they’re getting adequate amounts of vitamins and minerals.
The less common procedure, however, results in better blood sugar control and higher rates of diabetes remission than Roux-en-Y gastric bypass surgery. Researchers didn’t understand why until, in this study, Klein’s team followed 24 patients, half of whom had Roux-en-Y gastric bypass surgery and the other half, biliopancreatic diversion.
The gastric bypass group in the study had average body mass indexes (BMI) of 48. A person’s BMI is calculated using weight and height. A higher BMI increases risk of health problems related to weight; a BMI of 30, for example, is considered obese. Those who had biliopancreatic diversion had average BMIs of 56.
Bariatric surgeries at home and abroad
Surgeons performed the procedures overseas at Catholic University in Rome because biliopancreatic diversion is more commonly performed in Italy. In the US, surgeons performed some 228,000 bariatric procedures in 2017. Fewer than 3% were biliopancreatic diversion.
After surgery and a 20% loss of body weight, researchers measured the patients’ metabolic reactions to meals, with close attention paid to glucose levels, sensitivity to insulin, and how much insulin they secreted after eating.
The researchers found no difference in the benefit of surgery-induced weight loss to patients’ pancreatic function, in terms of insulin secretion, but patients who received biliopancreatic diversion surgery were more sensitive to insulin.
Klein notes that while the patients had obesity, none had a type 2 diabetes diagnosis. Researchers structured the study that way because they wanted to independently measure the insulin sensitivity after a meal, without potential complications caused by diabetes medications.
“This study demonstrates that biliopancreatic diversion has unique, beneficial effects on insulin action, independent of any weight loss,” he says.
As to whether the findings mean that surgery is preferable, Klein says that’s less clear. The main consideration, he says, should be patient safety.
“This study demonstrates additional metabolic benefits from biliopancreatic diversion, compared to Roux-en-Y gastric bypass,” he says. “But the type of bariatric surgery performed on any individual patient depends on many considerations, including an assessment of the effectiveness and safety of the procedure, patient preference, and the surgeon’s experience.”
Klein, chief of the geriatrics and nutritional science division, adds that Roux-en-Y gastric bypass provides considerable benefits in helping people lose weight and in treating type 2 diabetes but does not have the weight-loss-independent benefits on insulin sensitivity of biliopancreatic diversion.
The National Institute of Diabetes and Digestive and Kidney Diseases, the National Heart, Lung and Blood Institute of the National Institutes of Health, and the Pershing Square Foundation suppported the work.
