Weight-loss surgery has the side effect of improving type 2 diabetes. Now doctors are discovering why
IT WAS discovered by accident more than a decade ago that weight-loss surgery often led to a dramatic improvement in the control of type 2 diabetes, often before patients left the hospital.
Today, evidence of the connection is so solid that some doctors say surgery should be considered as a treatment for diabetes, regardless of a person’s weight.
“We thought diabetes was an incurable, progressive disease,” says Dr Walter J Pories, a professor of surgery at East Carolina University and a leading researcher on weight-loss surgery. “It . . . is a major cause of amputations, renal failure and blindness. This operation takes about an hour, and two days in hospital, and these people go off their diabetes medication. It’s unbelievable.”
As many as 86 per cent of obese people with type 2 diabetes find their diabetes goes or is much easier to control within days of having weight-loss surgery, according to 19 studies discussed earlier this year in the American Journal of Medicine. But experts still aren't sure why obesity surgery helps to resolve type 2 diabetes or how long the effect might last. And they disagree on how big a role surgery should have.
“We are going from seeing the results to understanding why it happens,” said Dr Santiago Horgan, director of the Center for the Treatment of Obesity at the University of California, San Diego.
This much is clear: patients who have weight-loss surgery begin to lose weight rapidly, which by itself improves type 2 diabetes, allowing diabetics to more easily control their blood glucose levels. But something else seems to be occurring, too.
There is strong evidence that surgery – especially gastric bypass surgery, which makes the stomach smaller and allows food to bypass part of the small intestine – causes chemical changes in the intestine, says Dr Jonathan Q Purnell, director of the Bionutrition Unit at Oregon Health Science University.
The small intestine has been thought of simply as the place where digestion occurs. But researchers now suspect it has other functions related to metabolism. Surgery somehow alters the secretion of hormones in the gut that play a role in appetite and help process sugar.
Multiple studies in humans and animals indicate that surgery triggers reductions in ghrelin, the hormone that stimulates hunger, and elevates levels of peptide YY and glucagon-like peptide-1, both of which act as appetite suppressants. Another theory is that surgery might alter the expression of genes that regulate glucose and fatty-acid metabolism.
“There are these known components that improve glucose metabolism,” Purnell says. “But there are very likely other things happening as well.”
The effect on diabetes can depend on the type of weight-loss surgery, says Pories, past president of the American Society for Metabolic and Bariatric Surgery. The highest rates of diabetes remission are seen in people who have gastric bypass – about 83 per cent.
But diabetes also tends to resolve or improve in 50 per cent to 80 per cent of people who have lap-band surgery, in which a band is placed around the top of the stomach to make it smaller. There is evidence that the effect occurs with a newer type of surgery called gastric sleeve, in which a portion of the stomach is removed so that it takes the shape of a tube or sleeve.
Evidence suggests the effect on diabetes can last for an extended period or even indefinitely, particularly if people don’t regain a lot of weight.
“There is durability, but we also know that some people do get the disease back,” Purnell says. “Weight rebound is probably one factor. We also know that diabetes is progressive. It may depend on how long you’ve been diagnosed. If it’s early on, I think durability may be better.”
It’s not clear yet why people have different responses. “There is some evidence that African-Americans don’t respond as well as Caucasians, and men don’t respond as well as women,” Pories says.
Despite the unknowns, the evidence that a majority of people experience long-term improvement in blood glucose control suggests the surgery could eventually play a greater role in the treatment of obese people with type 2 diabetes. The majority of American adults with type 2 diabetes are overweight.
Traditional medical guidelines, which insurers follow, state that weight-loss surgery should be restricted to patients with a body mass index of 35 or greater who have related health problems. But some think those don’t go far enough. Several studies are examining the benefits of surgery in people with a BMI of less than 35.
Studies from several countries show that surgery results in remission of diabetes for people who are not morbidly obese. There is even discussion of performing weight-loss surgery for people with type 2 diabetes who are not overweight.
In the US, weight-loss surgery is still largely viewed as a cosmetic procedure and obesity as a lifestyle issue. Moreover, weight-loss surgery carries risk. The death rate is about 1 per 200 operations, and severe complications can occur, including blood clots, infection, and the need for subsequent corrective surgery.
But a risk-benefit analysis published in April in the J ournal of the American Medical Associationby Purnell and a colleague suggests that if the number of gastric bypass operations performed on diabetic patients increased to 1 million per year, as many as 14,310 diabetes-related deaths might be prevented over five years.
Surgery also leads to other health benefits. Patients often see improvements in blood pressure, cholesterol, gastroesophageal reflux disease and sleep apnea.
“Doctors say, ‘If I can lower glucose by medications, why send patients to surgery?’,” Purnell says. “Surgery, however, allows people to have meaningful and sustained weight loss, and their diabetes is better.”
The discovery of the gut hormones that play a role in appetite and insulin regulation may lead to new medications, Pories says. “You can’t operate on 31 million Americans but if we understood this mechanism and the molecules secreted by the intestines that cause diabetes, then we can cure it with a pill. I would not be surprised if, in the next five years, we have new medications.” – (Los Angeles Times/Washington Post)
