Science News - September 10, 2011

very obese patients, he says, “the gauge is whether the risk of the present condition may be higher than the risk from the surgery itself. We think the risk of the condition is higher.”

Going all in

Like poker players pushing their chips into the center of the table, up to 70 percent of people in the United States who elect to have weight-loss surgery now go with gastric bypass. It’s a permanent change that diverts food around much of the stomach and the upper portion of the small intestine. Bypass surgery far outpaces gastric banding, a reversible operation that is the second most popular choice at about 20 percent. Other options exist but are much less common.

“I think gastric bypass will continue to be the mainstay of procedures because we understand how it works now,” says Robin Blackstone, a surgeon and president of the American Society for Metabolic and Bariatric Surgery who practices at the Scottsdale Healthcare Bariatric Center in Arizona. “It’s hitting obesity on so many fronts.”

The foremost front is food intake. Patients benefit not only from a smaller stomach, but also from chemical changes that occur as a result of the gastric switcheroo. Bypass surgery quells appetite by knocking back a hunger hormone called ghrelin, which is normally secreted by the stomach lining in response to food. And levels of an appetite stopper called peptide YY have been shown to increase five times as much in response to food among gastric bypass patients compared with levels in people who didn’t get the surgery. A Columbia University team reported last year in the Journal of Clinical Endocrinology & Metabolism that levels of a digestive hormone and appetite inhibitor called oxyntomodulin are doubled in diabetic gastric bypass patients only one month after surgery, whereas similarly obese people who lost weight by dieting saw no increase.

Hormonal switch flipping also appears to give bypass its power against type 2 diabetes, the adult onset kind.

When a person eats, the pancreas cranks out insulin — the hormone that regulates how cells burn sugars for energy. Patients with type 2 diabetes typically make insulin, but their cells resist its effects and leave too much sugar circulating in the blood.

Within weeks of gastric bypass, insulin resistance disappears in most patients, says John D. Scott, a surgeon at the Greenville Hospital System University Medical Center in South Carolina. “ Gastric bypass surgery kind of jump-starts that whole process,” he says.

In 2006, a research team at the Hospital Clínic Universitari in Barcelona established that only six weeks after gastric bypass surgery, patients (while still obese) make substantially more of the hormone glucagon-like peptide 1 in response to a meal than they did before having the operation. Shuttling food directly to the middle portion of the small intestine boosts GLP- 1, which keeps insulin-making cells alive, delays carbohydrate absorption and boosts insulin supplies as needed — roles that many scientists believe are instrumental in knocking back insulin resistance.

While GLP- 1 may do much of the dia-
betes-reversing job, more recent studies
suggest that it has helpers. A 2008 study
from researchers at East Carolina Uni-
versity in Greenville, N.C., found that
gastric bypass patients have a decrease
during the first year after surgery in
a compound called IKK-beta, which
is known to sabotage insulin signal-
ing. Increases in growth hormone seen
within six months of gastric bypass sur-
gery coincided with improved insulin
sensitivity. And changes in a gut hormone
called glucose-dependent insulinotropic
polypeptide also seem to contribute to
diabetes reversal.

Top two Gastric bypass redirects food around most of the stomach and the upper small intestine. Gastric banding, the next most popular weight-loss surgery, places a band around the stomach to limit its size. Bypass’ strengths come from hormonal switches ;ipped by diverted food.