Gastric bypass surgery in mice alters the microbial makeup of their gut, and these changes may contribute to the rapid weight loss experienced after the surgery, according to a new study appearing in the 27 March issue of the journal Science Translational Medicine.
Researchers found that transplanting microbes harvested from mice that underwent surgery, into mice with no gut bacteria, led to weight loss (up to 5% of body weight) and decreased fat tissue in the mice who received the transplants.
If confirmed in further studies in humans, these findings could someday lead to better non-surgical treatments for obesity.
“Our findings emphasize the importance of accounting for the influence of the trillions of microbes that inhabit our body when we consider obesity and other, complex diseases,” said Peter Turnbaugh, a postdoctoral researcher at Harvard University and co-author of the study.
Turnbaugh and colleagues observed changes in the abundance of two groups of microbes in the mouse gut following surgery, namely increased levels of Proteobacteria like E.coli and Verrucomicrobia. These bacteria are normally found at relatively low levels in healthy humans and rodents, and previous studies have shown that gastric bypass surgery can alter their abundance in the human and rat gut as well.
The researchers were surprised at how quickly and strongly surgery altered gut microbes (changes were observed after just one week) and how consistent these effects appear to be between mice, rats and humans. Changes in microbe populations occurred throughout the gastrointestinal tract, especially in the distal gut, far from the site of the surgery. The results indicate that gut microbe changes are not caused by weight loss or caloric restriction, but are unique to gastric bypass surgery itself.
The microbe community in the mouse gut differs depending on gastric bypass surgery. This image shows bacteria that are more abundant after bypass (red); after a sham surgery where the bypass was not performed (green); and in mice on a restricted diet (blue). [Click image to view larger version.] | Image courtesy of Science Translational Medicine/AAAS
The authors aren’t exactly sure how gut microbe changes promote weight loss, but one possible mechanism may be changes to the types of short-chain fatty acids produced in mice after surgery, which could affect metabolism or fat storage.
Read the abstract, “Conserved Shifts in the Gut Microbiota Due to Gastric Bypass Reduce Host Weight and Adiposity,” by A.P. Liou and colleagues.