Small Intestinal Bacterial Overgrowth in Patients with Roux-en-Y Gastric Bypass and One-Anastomosis Gastric Bypass

Obes Surg. 2022 Dec;32(12):4102-4109. doi: 10.1007/s11695-022-06299-z. Epub 2022 Oct 5.


Background: Small intestinal bacterial overgrowth (SIBO) is defined as an excessive growth and/or changed composition of bacteria in the small bowel. Obese patients are at increased risk of SIBO and related complications. The purpose of this study is to evaluate the incidence of SIBO after bariatric bypass procedures, connection between SIBO, symptoms, comorbidities, and liver pathology.

Methods: Patients underwent a hydrogen breath test with glucose substrate (25 g/200 ml of water). The demographic, anthropometric data, comorbidities, and symptoms were analysed with a questionnaire. In 45 patients, the NAFLD Activity Score was evaluated in liver biopsies.

Results: Glucose breath test was positive in 24/56 (43%) of patients and was associated with higher frequency of defecation (p = 0.022), lactose intolerance (p = 0.047), scleroderma (p = 0.042), irritable bowel syndrome (p = 0.018), and diabetes (p = 0.002). Mean NAFLD Activity Score in SIBO patients (n = 18) was 3.33 and 3.00 in non-SIBO patients (n = 27). In SIBO-positive cohort of patients, a statistically important trend in difference between NAS and difference to range value anti-Xa 4 h after subtherapeutic dose application was calculated.

Conclusions: The incidence of SIBO after bariatric surgery bypass procedures is alarmingly high (43%). The results of our study conclude that diagnosis cannot be set based on specific symptom and SIBO is related to reduced response to the application of LMWH. Mandatory SIBO screening and appropriate treatment would affect the clinical outcome of the underlying disease, improve it significantly, and prevent the development of its complications.

Keywords: Bariatric surgery; Glucose breath test; Liver injury; Obesity; One-anastomosis gastric bypass; Roux-en-Y gastric bypass; Small intestinal bacterial overgrowth (SIBO).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Gastric Bypass* / adverse effects
  • Glucose
  • Heparin, Low-Molecular-Weight
  • Humans
  • Non-alcoholic Fatty Liver Disease* / etiology
  • Obesity, Morbid* / surgery


  • Heparin, Low-Molecular-Weight
  • Glucose