Gastric bypass surgery

Gastric bypass surgery
One result of a study on obesity, gut microbiota, and weight-loss surgery indicates the surgery causes healthful changes in the microbes that live in the digestive tract and these changes are evident as long as ten years after surgery. Even more surprising, perhaps, is that the results of the pound-shedding surgery hint at being “contagious.”

Two Types of Bariatric Surgery

At the University of Gothenburg in Sweden, Fredrick Bäckhed and his team of research colleagues examined the gut microbiota of 14 women who had undergone gastric bypass (bariatric) surgery an average of 9.4 years earlier. Gut microbiota (also microbiome) is the bacteria and other microbes that naturally inhabit the human digestive tract and are instrumental to effective digestion and absorption of nutrients. The women shared many physical characteristics before surgery (percentage of excess weight, fat distribution, body composition, and such) and had all benefited from the similar number of pounds and amount of fat mass loss.

Seven of the women had undergone one type of bariatric surgery while the remaining seven had another type:

  • RYBG — Roux-en-Y gastric bypass
  • VBG — vertical banded gastroplasty

The Control Group

The gut microbiota from nine obese women matched by age, body mass index (BMI), and other factors (the control group) to that of the pre-surgical state of the 14 study patients were compared. The nine women in the control group (identified as OBS) had not had bariatric surgery. All gut microbiota samples were taken from fecal samples submitted by the study participants.

Striking Differences

The researchers discovered striking differences in the microbiota of the surgery patients when compared to the non-surgical controls. Genetic origins of hundreds of different gut microbial strains were tracked:

  • In the RYGB group, 928 strains were healthier (enriched, more abundant) and 60 were depleted when compared to that of the OBS control group.
  • In the VBG group, 682 strains were enriched and 33 were depleted compared to the OBS group.

By testing genetic origins of the gut microbiome, the research team was able to determine the healthy changes occurred after bariatric surgery.

Contagious Benefits

Recent studies have indicated fecal transplants from healthy donors into the intestinal tracts of patients with irritable bowel disease (IBD) were successful in reversing the disease state. The Swedish researchers used mice to see if the surgery-induced changes would produce similar results.

The researchers used laboratory mice specially bred to be “germ-free,” without any naturally occurring gut bacteria in their bodies. Some of the mice were treated with stool sample transfers from the surgical patients and some from the OBS control participants. The mice treated with samples from the RYGB and VBG groups had higher quality fat metabolism and less body fat accumulation than those getting samples from the OBS group.

These mice seemed to have benefitted from the healthy weight-maintenance characteristics of the after-surgery biome changes without undergoing surgery themselves.

This “contagious” transfer of benefits led Bäckhed to say, "Our findings are important in light of the growing epidemic of obesity and associated diseases. Since surgery always confers a risk, it is critical to identify non-surgical strategies. One potential strategy would be to devise novel probiotics based on our findings that can be supplied to obese individuals."


  1. Tremaroli, Valentina, et al. "Roux-en-Y Gastric Bypass and Vertical Banded Gastroplasty Induce Long-Term Changes on the Human Gut Microbiome Contributing to Fat Mass Regulation." Cell Metabolism 22.2 (2015): 228-38. Elsevier Inc. Web. 17 Aug. 2015.
  2. "Weight loss surgery benefits for gut microbiome last at least a decade." EurekAlert! American Association for the Advancement of Science (AAAS), 4 Aug. 2015. Web. 17 Aug. 2015.
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