Obesity Is Inversely Related to Hydrogen-Producing Small Intestinal Bacterial Overgrowth in Non-Constipation Irritable Bowel Syndrome

There have been inconsistent findings on the association of obesity and non-constipation irritable bowel syndrome (IBS). Small intestinal bacterial overgrowth (SIBO) with hydrogen (H₂) gas forming-microflora causes non-constipation IBS. But, the effect of H₂ producing SIBO on obesity in non-constipation IBS patients has not been studied yet. The aim of this study was to investigate the association between obesity and SIBO in non-constipation IBS patients. We reviewed the charts of patients who showed IBS symptoms along with the documented results of their lactulose hydrogen breath test (LHBT) for SIBO. Multivariate models were used to assess the association between obesity and SIBO. Four-hundred fifty-eight patients were retrospectively included in the study. Of the 485 IBS patients, 158 (30.7%) subjects had positive results for LHBT. Subjects without SIBO showed significantly higher levels of body mass index (24.8 vs. 23.3; P < 0.001) and waist circumference (86.5 vs. 82.7; P < 0.001) as compared to subjects with SIBO. In multivariate analysis, the odds ratios of SIBO were 0.396 (P = 0.018) for obesity and 0.482 (P = 0.021) for abdominal obesity. This is the first human study to demonstrate that obesity is inversely related to SIBO with H₂ gas production in non-constipation IBS patients.