Evidence that surgery can reverse diabetes is so compelling that new guidelines from the American Diabetes Association call for using procedures to treat diabetes, not just obesity. But the mechanism has remained a mystery.
It’s one of the most important mysteries of diabetes and obesity care: numerous studies have found that for some patients, bariatric surgery to promote weight loss also causes diabetes to retreat. The evidence is so compelling that in June, the American Diabetes Association (ADA) published guidelines that recommend surgery to correct diabetes, not just obesity.
But there’s been equal agreement that diabetes goes into remission for reasons that aren’t fully explained by weight loss—often blood sugar levels plummet in advance of patients reaching their goal weight. The question is, why?
An experiment published in The American Journal of Pathology suggests that bacteria in the gut play a role. What’s more, the researchers found, surgery may be an option for both diabetes that’s tied to genetic factors and cases that result from poor diet.
Researchers led by Xiang Gao, PhD, of Nanjing University in China used genetically modified mice to see what precisely happens after a duodenum-jejunum bypass (DJB) procedure. “We found that DJB surgery induced gut microbiota alternations, which may be the key reason for diabetes remission after bariatric surgery,” he said.
“Our data indicate that suppressed inflammation is the result, not the cause, of diabetes reversal in these genetically modified mice,” he said. The mice had been modified with a genetic mutation of brain-derived neurotrophic factor, which regulates metabolic balance. This caused the mice to possess symptoms such as insulin resistance, high lipid levels, and obesity.
When the study team examined gut bacteria before and after surgery—in both the surgical and control groups—they found that surgery promoted growth of beneficial gut bacteria while reducing more harmful ones. The study also showed that inflammation indicators in the liver dropped, although this happened after insulin sensitivity improved. Inflammation has long been considered a culprit in diabetes.
Gao recommends more studies to figure out how gut bacteria manage a person’s nutrient absorption.
Jiang S, Wang Q, Huang Z, et al. Gastric bypass surgery reverses diabetic phenotypes in Bdnf-deficient mice [published online July 11, 2016]. Am J Pathol. 2016; doi:10.1016/j.ajpath.2016.04.009.