Distinguishing Between Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome

Although small intestinal bacterial overgrowth (SIBO) and irritable bowel syndrome (IBS) share many of the same symptoms, SIBO affects the small intestine and IBS affects the large intestine.¹ A team of researchers from the Department of Gastroenterology at Perking Hospital in Beijing, China designed a study to better differentiate SIBO and IBS. The study examined SIBO and IBS symptoms and common bacteria present in patients’ gastrointestinal tracts.²

Man with digestive illness | Image credit: eddows | stock.adobe.com

The study consisted of 3 patient groups: healthy controls, patients with IBS, and patients with SIBO. The patients filled out symptom questionnaires and provided stool samples that the team analyzed for bacteria strains.²

Patients within the IBS group reported more about their symptoms than bowel habits. They experienced abdominal pain, bloating, and diarrhea. The most common bacteria in the IBS group were Lachnoclostridium, Escherichia-Shigella, and Enterobacter. Patients with SIBO reported more about their bowel habits than symptoms and the most common bacteria in this group were from the Ruminococcaceae Group.²

During the study, the researchers found that major depression disorders were higher in the IBS and SIBO patients compared with the healthy controls. The constant gastrointestinal discomfort in IBS and SIBO can aggravate depressive disorders. Additionally, they found that the IBS group’s consumption of soluble fiber improved their symptoms and intake of insoluble fiber worsened their symptoms.² Soluble fiber attracts water and turns into a gel in the digestive tract, which slows digestion. Insoluble fiber adds bulk to the stool, which increases stool frequency and aggravates IBS patients’ diarrhea.³

Many patients with SIBO had decreased their carbohydrate intake in efforts to decrease their bloating. The researchers found that the gut microbiota differences between IBS and SIBO can serve as important biomarkers to distinguish the 2 conditions.²

The researchers mentioned some limitations of the study, such as using outdated criteria for diagnosis of IBS patients. Rome III criteria was used instead of Rome IV because it was deemed appropriate for the patient population in the study. The Rome IV criteria require more frequent symptoms for patients to be diagnosed with IBS.⁴ The patient population in China experienced Rome III criteria: abdominal pain, discomfort, and bloating at least 3 times a month. The patients’ symptoms may differ from other populations. Additionally, patients with SIBO were only diagnosed using the breath test, which could result in some false positives. The study did not use the gold standard for SIBO diagnosis, the intestinal aspirate culture.

REFERENCES

1. SIBO similar to IBS, but in small intestine. UCLA Health. May 2, 2022. Accessed August 26, 2024. https://www.uclahealth.org/news/article/sibo-similar-to-ibs-but-in-small-intestine 

2. Lu S, Chen Y, Guo H, Liu Z, Du Y, Duan L. Differences in clinical manifestations and the fecal microbiome between irritable bowel syndrome and small intestinal bacterial overgrowth. Dig Liver Dis. doi:10.1016/j.dld.2024.07.011

3. Soluble vs. insoluble fiber. Mount Sinai Health System. Accessed August 30, 2024. https://www.mountsinai.org/health-library/special-topic/soluble-vs-insoluble-fiber.

4. Rome III to rome IV: Updates and developments. Gastrointestinal Society. August 4, 2020. Accessed August 29, 2024. https://badgut.org/information-centre/a-z-digestive-topics/rome-iv/.