Tremaroli et al. reported that bariatric surgery for obesity, whether gastric bypass or vertical banded gastroplasty, induced a significant and sustained change in the gut microbiome of 14 women for at least a decade.


The researchers observed that both surgical procedures induced similar and durable changes, and were found not dependent on body mass index. Among the changes in the gut microbiome were genetic adaptation to the new environment (including an increase in sugar metabolism and glycolysis), a decrease in the ratio of short-chain fatty acids to branched-chain fatty acids, and an increase in the dihydroxylation of primary bile acids. In relation to the microbiota composition there were detected significant differences between samples from gastric bypass and severely obese subjects. In particular, several species in Gammaproteobacteria class presented higher levels, while three species in the Firmicutes phylum (Clostridium difficile, C. hiranonis and Gemella sanguinis) were lower in gastric bypass samples, compared to severely obese subjects.

Moreover, the role of the gut microbiota in the weight loss was confirmed elegantly by transplanting into germ-free mice the microbiota of obese patients after gastric bypass, vertical banded gastroplasty, or no surgery. Post-surgery microbiota reduced body fat and lowered the respiratory quotient in the mice, indicating decreased oxidation of carbohydrates and increased oxidation of fat. The research showed gut microbiota change is a key factor in the success of bariatric surgery to control obesity.



Tremaroli V, et al. (2015) 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), pp. 228–238. doi:10.1016/j.cmet.2015.07.009.