Gut Bacteria Differences Found in IBS Patients With Bacterial Overgrowth
- Authors
- Xiufang Cui, Haiyang Wang, Hongjie Zhang, Xinmei Zhang
- Journal
- Medicine
- Year
- 2026
- DOI
- 10.1097/MD.0000000000049955
- Study Type
- Human
- Outcome
- Neutral
- Peer Reviewed
- Yes
- Country
- China
- Health Condition
- Irritable Bowel Syndrome (IBS)
- Body System
- Gastrointestinal
TL;DR
IBS patients with SIBO showed modest differences in fecal microbiota, particularly lower Firmicutes abundance, which was associated with abdominal symptoms and visceral sensitivity.
Key Finding
IBS patients with SIBO had significantly lower levels of Firmicutes (a major group of gut bacteria) compared to healthy controls, and lower Firmicutes levels correlated with more severe abdominal pain and IBS symptoms.
Summary
This study examined differences in gut bacteria between people with irritable bowel syndrome (IBS) who also had small intestinal bacterial overgrowth (SIBO) versus those who did not. SIBO was detected using a hydrogen breath test, which measures hydrogen gas produced by bacteria in the gut. Researchers found that IBS patients with SIBO had lower levels of a bacterial group called Firmicutes, and that lower Firmicutes levels were linked to worse abdominal pain and IBS symptoms. The study included 52 participants total.
Practical Takeaway
This study does not directly test hydrogen water as a treatment. However, it used a hydrogen breath test as a diagnostic tool and highlights how gut bacteria imbalances relate to IBS symptoms. For someone interested in hydrogen research, this study is relevant background science — it suggests that gut bacterial activity and hydrogen gas production are measurable markers of digestive health, though no conclusions about hydrogen water can be drawn from this research.
Abstract
Small intestinal bacterial overgrowth (SIBO) is common in irritable bowel syndrome (IBS) and has been proposed as an etiologic factor. This study aimed to identify potential fecal microbiota profiles in patients with IBS and SIBO. A total of 52 subjects were enrolled in this study, of whom 18 were normal controls (NCs). Patients were divided into 2 groups: IBS with SIBO (IBS.SIBO+) and IBS without SIBO (IBS.SIBO-). SIBO was identified using a standard glucose hydrogen breath test. The IBS symptom severity scale, abdominal pain, and health-related quality of life were evaluated using questionnaires. Rectal balloon distension was used to measure visceral sensitivity. Fresh fecal samples were collected, and 16S rRNA gene sequencing analysis was performed to evaluate the structure and diversity of the microbiota among different groups. Correlation analysis was performed to assess the relationship between specific flora and abdominal pain, visceral sensitivity, and quality of life. The richness of the intestinal microbiota in the IBS.SIBO- group was significantly lower than that in the IBS.SIBO+ group (P = .012). At the phylum level, the relative abundance of Firmicutes decreased significantly in fecal samples collected from IBS with SIBO compared to those in the NCs and IBS without SIBO groups. No significant difference was found between the NCs and IBS without SIBO groups, although the phylum type showed a decreasing trend in the latter. At the genus level, Fusobacterium (P = .01) was significantly less abundant in the IBS with SIBO group than in the NC group; however, no significant difference was found between the IBS with SIBO and IBS without SIBO groups. The relative abundance of Firmicutes correlated negatively with the abdominal pain scale (r = 0.436, P = .026) and the IBS symptom severity scale (r = 0.494, P = .010), whereas a positive correlation was found between the defecation distress threshold and Firmicutes (r = 0.458, P = .019). Fecal microbiota showed mild dysbiosis in patients with IBS and SIBO compared to those without SIBO. The decreased abundance of Firmicutes may be related to IBS symptoms and abdominal pain.