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ibs and sibo
By Dominick Hussey 0 Comments Gut Health, Irritable Bowel Syndrome, SIBO

IBS and SIBO: Understanding the Connection

Irritable bowel syndrome (IBS) and small intestinal bacterial overgrowth (SIBO) are two gastrointestinal disorders that share overlapping symptoms, thus making diagnosis and treatment challenging. Emerging research suggests a significant connection between the two, moreover with some experts proposing that SIBO may be an underlying cause of IBS in a subset of patients (Trio Smart., 2025). Accordingly, this article explores the relationship between SIBO and IBS, examining symptoms, diagnostic methods, treatment approaches, and current debates in the medical community.

Table of contents

Understanding IBS and SIBO

What Is IBS?

IBS is a functional gut disorder generally characterized by chronic tummy pain, bloating, and altered bowel habits (diarrhea, constipation, or a mix of both) without seen structural issues (Mayo Clinic, 2025). IBS affects approximately 10–15% of the global population and is more common in women than men (Canavan et al., 2014).

What Is SIBO?

SIBO occurs when bacteria grows in the small bowel, which typically has relatively low bacterial counts compared to the colon (Mayo Clinic, 2025). This overgrowth can lead to fermentation of carbohydrates, producing gas and leading to symptoms such as bloating, diarrhea, and poor absorption of nutrients (Mayo Clinic, 2025).

The Overlapping Symptoms of SIBO and IBS

The clinical presentations of SIBO and IBS are markedly similar, subsequently leading to poor diagnosis. For instance, common symptoms shared by both conditions include:

  • Abdominal bloating and distension
  • Abdominal pain or discomfort
  • Altered bowel habits (diarrhea, constipation, or mixed)
  • Excessive gas

Because of this overlap, some researchers hypothesize significant IBS cases may be really SIBO (Trio Smart., 2025).

Evidence Linking SIBO and IBS

Prevalence of SIBO in IBS Patients

Several studies have found a higher liklehood of SIBO in IBS patients compared to healthy controls. A study summarizing several clinical trials by Shah et al. (2010) reported that up to 78% of IBS patients tested positive for SIBO using breath testing, though this figure varies depending on diagnostic criteria.

Mechanisms Connecting SIBO and IBS

There are several mechanisms that connect IBS and SIBO, for example:

  1. Altered Gut Motility – Slow bowel transit (common in IBS-C) may promote the overgrowth of bacteria by subsequently allowing bacteria to grow in the small bowel (Rao et al., 2015).
  2. Immune Activation and Low-Grade Inflammation – SIBO may trigger immune responses, so worsening IBS symptoms (Barbara et al., 2016).
  3. Fermentation and Gas Production—Bacterial fermentation of carbohydrates leads to hydrogen and methane production, thus contributing to bloating and pain (Pimentel et al., 2020).

Diagnosing SIBO in IBS Patients

Breath Testing

The most common diagnostic tool for SIBO is the hydrogen and methane breath test, where patients ingest lactulose or glucose and exhaled gases are measured (Rezaie et al., 2017). Elevated hydrogen or methane levels suggest bacterial overgrowth. However, breath testing has limitations, including false positives and variability in interpretation (Saad & Chey, 2014).

Small Intestine Aspirate and Culture

The gold standard for SIBO diagnosis is jejunal aspirate culture, where fluid from the small intestine is collected and analyzed for bacterial counts (>10³ CFU/mL is diagnostic) (Khoshini et al., 2008). However, this method is invasive and not routinely used.

Challenges in Diagnosis

  • Symptom overlap with IBS makes it challenging to distinguish between the two without testing.
  • False-negative breath tests due to rapid transit or improper preparation.
  • Lack of standardized diagnostic criteria for SIBO (Sachdev & Pimentel, 2013).

Treatment Approaches

Antibiotic Therapy

The primary treatment for SIBO is antibiotics, such as rifaximin, which targets gut bacteria without significant systemic absorption (Pimentel et al., 2011). For instance, studies show that 50–60% of IBS patients improve after rifaximin treatment, supporting the SIBO-IBS link (Acosta & Camilleri, 2015).

Dietary Modifications

  • Low-FODMAP Diet – Reduces fermentable carbohydrates that feed bacterial overgrowth (Gibson & Shepherd, 2010).
  • Elemental Diet – A liquid diet that starves bacteria, sometimes used in refractory SIBO (Takakura & Pimentel, 2020).

Prokinetics

Since impaired motility contributes to SIBO, prokinetic agents like prucalopride or erythromycin may help prevent recurrence (Rao et al., 2015).

Controversies and Limitations

Does SIBO Cause IBS?

While some studies support the SIBO-IBS connection, others argue that breath testing is unreliable and that SIBO may be a consequence of IBS rather than a cause (Ford et al., 2020). Additionally, not all IBS patients respond to antibiotic therapy, suggesting heterogeneity in the disorder.

Overdiagnosis of SIBO

Some experts caution against over-reliance on breath tests, which can produce false positives (Simren et al., 2018). The Mayo Clinic highlights that non-invasive breath testing lacks standardization, leading to potential misdiagnosis (Mayo Clinic, 2023).

Conclusion

The relationship between SIBO and IBS remains complex and incompletely understood. While evidence suggests that SIBO may contribute to IBS symptoms in a subset of patients, further research is needed to clarify diagnostic criteria and optimize treatment. For now, clinicians should consider SIBO testing in IBS patients who do not respond to conventional therapies, particularly those with bloating and diarrhea-predominant symptoms.

References

  1. The IBS & SIBO Connections. Trio-smart. Published 2025. Accessed April 5, 2025. https://www.triosmartbreath.com/ibs-and-sibo-connections.
  2. ‌Irritable bowel syndrome – Symptoms and causes. Mayo Clinic. Published 2025. Accessed April 5, 2025. https://www.mayoclinic.org/diseases-conditions/irritable-bowel-syndrome/symptoms-causes/syc-20360016
  3. ‌Canavan C, West J, Card T. The epidemiology of irritable bowel syndrome. Clin Epidemiol. 2014;6:71-80. Published 2014 Feb 4. doi:10.2147/CLEP.S40245
  4. Shah ED, Basseri RJ, Chong K, Pimentel M. Abnormal breath testing in IBS: a meta-analysis. Dig Dis Sci. 2010;55(9):2441-2449. doi:10.1007/s10620-010-1276-4

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