Small Intestinal Bacterial Overgrowth: Clinical Presentation in Patients with Roux-en-Y Gastric Bypass

Obes Surg. 2021 Feb;31(2):564-569. doi: 10.1007/s11695-020-05032-y. Epub 2020 Oct 12.


Background: Small intestinal bacterial overgrowth (SIBO) is defined by an increased number of bacteria measured via exhaled hydrogen and/or methane gas following the ingestion of glucose. This condition is prevalent following abdominal surgery, including Roux-en-Y gastric bypass (RYGB), and associated with a variety of non-specific abdominal symptoms, often requiring an extensive diagnostic work-up.

Aim: To assess the frequency that individuals with RYGB anatomy are diagnosed with SIBO and if they are more likely to report specific gastrointestinal (GI) symptoms compared to individuals with native anatomy.

Methods: This large matched cohort study evaluated patients with GI symptoms who underwent a glucose breath test (GBT) for SIBO evaluation, utilizing 1:2 matching between RYGB and native anatomy. Patients with positive GBT were included in univariate and multivariate analyses to distinguish the presence of ten specific GI symptoms between RYGB and native anatomy.

Results: A total of 17,973 patients were included, where 271 patients with RYGB were matched to 573 patients with native anatomy that underwent GBT. Patients with RYGB anatomy and a positive GBT (199; 73.4%) as compared to those with native anatomy and a positive GBT (209; 36%) more often reported nausea, vomiting, bloating, and diarrhea. There were no differences between the two groups in the report of heartburn, regurgitation, chest pain, gas, or constipation.

Conclusions: SIBO is common in patients with RYGB and more commonly report nausea, vomiting, bloating, and diarrhea. The results of this study suggest that the report of these symptoms in RYGB should prompt early evaluation for SIBO.

Keywords: Diarrhea; Nausea; Roux-en-Y gastric bypass; Small intestinal bacterial overgrowth; Vomiting.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Breath Tests
  • Cohort Studies
  • Constipation
  • Gastric Bypass* / adverse effects
  • Humans
  • Obesity, Morbid* / surgery