Diabetes Forecast

Weight-Loss Surgery's Effects on Diabetes

Researcher: Blandine Laferrère, MD
Occupation: Assistant Professor of Medicine, Columbia University College of Physicians and Surgeons, and Research Associate, Obesity Research Center
Focus: Endocrinology, diabetes, and nutrition
ADA Research Funding: Clinical Translational Research Award

No diet can match surgery when it comes to dramatic weight loss. In the past decade, the popularity of bariatric surgery has soared, and doctors now perform about 200,000 operations a year in the United States alone to help people trying to lose lots of weight.

There are two basic types of weight-loss surgery. The first, adjustable gastric banding, involves placing around the stomach a fluid-filled belt that can be adjusted by a doctor using a port inserted just under the skin. Banding is reversible and requires attention from both patient and doctor; the band needs to be adjusted regularly. The other, more popular version of bariatric surgery is the gastric bypass. A bypass operation shrinks the size of the stomach by over 90 percent, leaving it the size of an egg. Importantly, it also routes food around part of the small intestine, which reduces how much food the body absorbs. Both procedures result in extensive weight loss. That alone has a positive effect on health, including the toll type 2 diabetes can take on the body.

But with gastric bypass, there's more to it than that. Gastric bypass "makes [people with diabetes] lose weight but also seems to have an effect independent of weight loss on diabetes resolution," says Blandine Laferrère, MD, an endocrinologist at the Obesity Research Center in New York.

The effects are remarkable: Nearly 80 percent of patients with type 2 diabetes who have gastric bypass go into remission. "It's a little bit of a miracle," Laferrère says. "If the surgery is successful, patients are off medication, they don't have to check finger sticks, their mortality goes down." The change has to do with much more than lost pounds: Remission with gastric banding is less frequent, even when the weight loss is comparable.

With the help of a grant from the American Diabetes Association, Laferrère is comparing the two types of surgery to try to figure out what it is that makes gastric bypass so effective. Her research involves recruiting two dozen patients about to undergo either gastric bypass or banding and monitoring them closely before and after the surgery. The key to the gastric bypass "miracle" may be the elaborate signaling that goes on all through the digestive process, sending messages from the intestine to the cells in the pancreas that secrete insulin. "The gut is really important," Laferrère says, particularly chemicals called peptides that are released in the intestine during digestion. Peptides tell the body food has arrived and are responsible for alerting the pancreas to begin pumping out insulin. (Certain peptides also send a "full" signal to the brain, prompting you to stop eating.)

Yet diabetes can derail this signaling. "Peptides are blunted or not working well in patients with diabetes," Laferrère says. "Fifty percent of insulin secretion depends on gut peptides, and that's blunted to 10 or 20 percent during type 2 diabetes." It's counterintuitive, but doctors have discovered that by circumventing part of the stomach and the first part of the small intestine, gastric bypass surgery markedly improves the body's peptide signaling system, sometimes reversing the effects of type 2 diabetes entirely and restoring the secretion of peptides to normal levels.

Laferrère says different theories seek to explain gastric bypass surgery's impact. Some researchers, for example, think the smaller stomach passes food more quickly to the lower part of the intestine, which has more peptide-producing cells. Others argue there's something in the duodenum, a part of the small intestine that's bypassed during the surgery, that inhibits peptide production.

Naturally, the striking results have prompted many doctors to promote gastric bypass surgery for patients who are very heavy and have type 2 diabetes. Gastric bypass is permanent and more invasive than gastric banding, which is performed with less invasive surgery and can be reversed. "The bias in the surgical field is that patients with type 2 should have bypass, because it's so effective against diabetes," Laferrère says.

But the "cure" has serious risks and side effects: "Independent of superb weight loss and diabetes remission, bypass has its disadvantages," Laferrère says. Because parts of the intestine that help the body absorb food are bypassed, patients can have trouble absorbing enough vitamins. The surgery itself has risks, too: about 1 percent of patients die, roughly the same proportion as in hip replacement surgery.

As Laferrère searches for clues as to why gastric bypass works so well, she says, "The big picture is to understand how surgeries work on diabetes remission, with the hope that we could come up with less invasive surgeries or medication that could mimic the effect." That way, people with type 2 diabetes might someday be able to take advantage of gastric bypass's benefits without the surgery's risks.

For more on weight-loss surgery or to read four stories on life after surgery, click here.

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