Diabetes Forecast

What’s New in Weight-Loss Surgery?

The procedures show dramatic results—and raise hopes for more progress

By Erika Gebel Berg, PhD , ,
What’s New in Weight-Loss Surgery?


I’ve had more energy. I feel good. I love the way I look.
—Marla Evans, who had gastric bypass surgery

It’s hard to dispute the fact that in the fight against type 2 diabetes, weight-loss surgery trounces medication and lifestyle changes in severely obese people. Six years after weight-loss surgery, half of people with type 2 diabetes maintained an A1C below the diabetes diagnosis threshold of 6.5 percent without needing to take diabetes medication, a 2013 study in the Annals of Surgery found. No other therapy or lifestyle intervention comes close to matching those results. An additional third of participants had A1Cs at least a point lower than where they’d started out.

Even with these remarkable outcomes, weight-loss surgery, also called bariatric surgery, isn’t for everyone with type 2. In the study described above, participants’ average body mass index (BMI, an estimate of total body fat) was 49. For reference, a person who is 5-foot-5 and weighs 295 pounds has a BMI of 49. So make no mistake: The procedures are now designed to treat life-threatening obesity, although some surgeons are performing experimental surgeries on less-obese people with diabetes. Currently, though, the American Diabetes Association recommends that weight-loss surgery be considered only for people with type 2 who have a BMI of 35 or higher. These surgical procedures can have serious complications, such as malnutrition, bowel obstructions, infection, and, in rare cases, death. In addition, weight-loss surgery has other drawbacks; for example, some recipients need to follow a strict diet for life.

But what if you could get surgery’s benefits without going under the knife? That’s the dream of scientists who are studying weight-loss surgery’s dramatic effect on type 2 diabetes. For now, it’s an open question. Researchers continue to look at various factors to explain why weight-loss surgery improves blood glucose levels. The candidates include: weight loss, insulin, other hormones, the small intestine, and “friendly” bacteria in the intestines, known as gut microbes.

Weight Loss

Weight loss is almost certainly part of the reason blood glucose levels improve after the surgical procedures, says Sangeeta Kashyap, MD, associate professor of medicine at Cleveland Clinic Lerner College of Medicine. About 80 percent of people with type 2 diabetes are overweight or obese, and extra body fat is a well-known risk factor for developing the disease. There’s much evidence that weight loss can improve blood glucose control and prevent type 2.

People who have weight-loss surgery tend to rapidly lose a significant amount of excess weight. The amount of weight lost after surgery varies, but people can typically lose half their excess body weight or more. Even with such significant weight loss, though, dropping pounds doesn’t seem to be the whole story behind remission of type 2 diabetes.

Remarkably, some people with type 2 wake up from weight-loss surgery with the ability to maintain normal blood glucose levels without medication and before weight loss occurs—a transformation that scientists are eager to explain. Evidence now suggests that the rapid normalization of blood glucose after surgery may have to do with the extremely low-calorie diet a person eats during recovery and not some sort of magic. A small 2013 study in Diabetes Care found that feeding a post-surgery diet to people with type 2 diabetes who hadn’t had weight-loss surgery lowered their blood glucose as much as surgery can. This suggests that diet and not surgery may be behind these early effects, though more studies are needed to confirm this explanation.


Pound lost for pound lost, “you still see extra-special effects” from surgery, says Kashyap, when it comes to diabetes. “There is some evidence to suggest there are effects on beta cells that are independent of weight loss.” Type 2 diabetes is caused by a combination of the body becoming resistant to insulin and the beta cells of the pancreas failing to produce enough insulin to keep blood glucose levels in a normal range. A 2011 study in the journal Obesity compared 14 people with type 2 who’d lost the same amount of weight with surgery or through a low-calorie diet. The researchers found that surgery led to greater improvements in insulin sensitivity and insulin production than did weight loss from dieting. So weight-loss surgery helps the body make more insulin and respond to insulin better, but researchers still don’t know how surgery accomplishes the feats.

Other Hormones

The gut does more than turn food into fuel; it produces hormones that “talk” to the pancreas, the brain, and fat tissue to help the body use energy efficiently. Start cutting into the gut, and that hormone production may be altered. Scientists are looking into whether weight-loss surgery alters gut hormones in ways that may explain how such procedures improve blood glucose levels.

Weight-loss surgery increases hormones called incretins, according to blood tests of people with type 2 diabetes done before and after surgery. These gut hormones spur the production of insulin by the pancreas after a meal. A 2013 study in the Journal of Clinical Endocrinology & Metabolism found that weight-loss surgery doubled the amount of GLP-1, a type of incretin hormone, the gut produced after a meal. Several type 2 medications, such as exenatide (Byetta) and sitagliptin (Januvia), work by boosting GLP-1 activity in the body. This suggests that hormonal changes could be behind surgery’s special benefits in people with type 2.

The Small Intestine

The most common type of weight-loss surgery is gastric bypass, which involves rearranging the digestive tract. In this procedure, a surgeon divides the stomach, creating a small upper pouch that severely restricts how much food one can comfortably eat. A part of the small intestine is then brought up and attached to the stomach pouch, bypassing a large portion of the small intestine. This causes the body to absorb less food.

Gastric bypass surgery stands out as particularly beneficial for type 2—resulting in more weight loss and better blood glucose levels—compared with other types of weight-loss surgery that leave the intestine intact. These include gastric banding, a procedure that wraps an adjustable belt around the stomach and helps the recipient feel full with less food. Because gastric bypass is the most effective weight-loss surgery, scientists are looking into whether it lowers blood glucose levels by rearranging the small intestine.

Nima Saeidi, PhD, a research fellow in surgery at Harvard Medical School, performed gastric bypass surgery on rats with type 2 diabetes, then analyzed the rodents’ intestines. She discovered that the part of the intestine that’s surgically connected to the upper stomach pouch undergoes profound changes after surgery. The intestinal cells in this area begin gobbling up glucose from the bloodstream, which could explain at least part of why blood glucose levels drop in people who have gastric bypass surgery.

What’s more, the new glucose uptake happens without the help of insulin. “This suggests that the remission of diabetes could be independent of insulin action and pancreatic function,” says Saeidi, which would be good news for people who don’t produce much insulin. The implication is that obese people with type 1 diabetes could also get special benefits from weight-loss surgery. Saeidi’s collaborators are planning to study human intestines to see if they also begin to consume extra glucose after gastric bypass surgery.

Gut Microbes

Rearranging the gut can have a big impact on the organisms that call your intestines home. Researchers want to know if these changes can affect blood glucose levels. Friendly microbes that live in the gut help with digestion, vitamin production, and other key functions. Some evidence suggests that obesity and type 2 diabetes are caused in part by gut microbes gone awry.

 A 2013 study in Science Translational Medicine asked whether changes to the gut microbes from surgery aid weight loss and improve blood glucose control. Researchers performed gastric bypass on obese diabetic mice. Then they removed some of the rodents’ gut microbes and transferred them to lean, healthy mice that didn’t have the surgery. Those mice lost weight, suggesting that the changes to gut microbe populations may independently boost weight loss. The mice also showed less insulin resistance, suggesting that microbes may be involved in the diabetes benefits of surgery.

Marla Evans: diabetes-free after gastric bypass

Marla Evans, 57, of South Euclid, Ohio, had never heard of gastric bypass surgery until her phone rang seven years ago. Someone from the Cleveland Clinic asked if she would consider participating in a weight-loss surgery study for people with type 2 diabetes. Evans had been diagnosed with diabetes six years before, at the age of 44. “I was a denial diabetic,” she says. “I was just on pills, but I was not going to follow the rules.”

Marla Evans

The same week she got the call, an acquaintance from church had impressed upon her that diabetes was a “silent killer” and shouldn’t be taken likely. So, Evans decided to “go for it” and join the study. She was randomly assigned to a group that would have gastric bypass surgery. Before anyone lifted a scalpel, Evans visited a nutritionist, who told her about strict post-surgery dietary rules, and a psychiatrist, who assessed whether she “was prepared to follow the rules and be able to learn to eat all over again.” She said she was, and the surgery was on.

Not long after she woke up from surgery, a doctor tested Evans’s blood glucose. “I had no sign of diabetes,” she says. Her glucose levels have continued to stay in the nondiabetic range. She dropped from 220 to 140 pounds in 4½ months. “At 140, I was way too thin,” she says. “Now, I’m back to 155 and have stayed there for three years.” Evans does get physically sick sometimes if she eats too fast. She also experiences “dumping” syndrome, in which undigested food moves from the stomach to the small intestine too quickly, causing diarrhea.

To avoid such side effects and stay well nourished, Evans always starts her meals with a protein food before moving on to vegetables or starches. With gastric bypass surgery, malnutrition is a real concern. “I have a shelf of vitamins I have to take my whole life,” she says. Evans has other rules, too: Avoid carbonated beverages and most dairy; don’t drink fluids with meals or a half hour before and after eating; eschew straws to curb liquid intake; put the fork down after every bite to ensure slow eating. But Evans says following the rules has been worth it: “I’ve had more energy. I feel good. I love the way I look.”

The Five W’s of Weight-Loss Surgery

Who? Adults with a body mass index (BMI, an estimate of total body fat) of 35 or greater who have type 2 diabetes may consider weight-loss surgery, according to American Diabetes Association recommendations, especially if they have trouble controlling blood glucose or other serious health problems with lifestyle and medication.

What? Gastric bypass surgery, the most common type of weight-loss surgery, involves restructuring the digestive tract. Less common surgeries that restructure the intestines are biliopancreatic diversion and duodenal switch. Another type of surgery, gastric banding, uses a belt to shrink the stomach; it has fallen out of favor since a 2011 study found the procedure had poor long-term outcomes. A surgery that is growing in popularity is sleeve gastrectomy, which turns the football-shaped stomach into something about the size and shape of a banana.

Where? It may be wise to find a surgeon with a lot of experience. A 2013 study rated the surgical skills of 20 bariatric surgeons and found that those who’d performed the most operations had patients with fewer complications.

When? People who have weight-loss surgery within five years of developing type 2 diabetes have a higher rate of diabetes remission than those who have the procedure after a longer time with the disease.

Why? Because weight-loss surgery reduces the risk of death and improves type 2 diabetes. Severely obese people have an 89 percent lower risk of death over the first five years after weight-loss surgery than people with similar characteristics who don’t have the surgery. Bariatric surgery is also associated with an 82 percent lower risk for cardiovascular disease. Most people with type 2 diabetes are able to reduce or eliminate diabetes medication after weight-loss surgery.

Laparoscopic Surgery

Many weight-loss procedures are performed laparoscopically, which means that a surgeon uses several small incisions instead of a single large one to access the digestive tract. The surgeon inserts a laparoscope, a small snake-like camera, into the incision to help perform the procedure.  Laparoscopic surgeries typically have shorter recovery times and are less painful than standard surgeries.



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