SIBO and Probiotics: Understanding the Gut Microbiome Connection

Small intestinal bacterial overgrowth (SIBO) is a fairly common condition that can disrupt digestion and trigger uncomfortable symptoms. With an estimated 2.5–22% of the population affected, and risk increasing with age and comorbidities, SIBO is a key area in gut health research^1,2. Read on to learn more about SIBO, how it affects the gut, common symptoms, current treatment approaches and the role of probiotics for SIBO.

What is SIBO?

SIBO is defined as an excessive, abnormal increase of bacteria within the small intestine, typically involving types of bacteria normally found in the large intestine. The proximal small intestine usually contains very few organisms, maintained by defence mechanisms such as gastric acid and peristalsis³. When these defences fail, colonic microbiota can colonise the small intestine and have adverse effects on gut and overall health. SIBO is commonly diagnosed through specialised testing such as microbial culture and breath testing⁴.

SIBO can be broadly categorised by the type of gas-producing microorganism driving the overgrowth. Current consensus recognises three main subtypes and one mixed presentation subtype⁵:

• Hydrogen-dominant SIBO: The most common form of SIBO. Anaerobic bacteria such as Escherichia coli or Klebsiella pneumoniae ferment dietary carbohydrates in the small intestine and produce hydrogen gas. It is typically diagnosed through lactulose or glucose hydrogen breath tests.
• Intestinal methanogen overgrowth (IMO): Also known as methane-dominant SIBO. It is driven by archaea, most commonly Methanobrevibacter smithii, rather than bacteria. These microbes consume hydrogen produced by other microbes and convert it to methane gas, which slows intestinal transit. It is usually diagnosed using a methane breath test.
• Intestinal sulfide overproduction (ISO): Also known as hydrogen sulfide SIBO. It involves sulfate-reducing bacteria, such as Desulfovibrio species, that generate hydrogen sulfide gas. Standard breath tests do not measure hydrogen sulfide, so ISO has historically been difficult to diagnose. Emerging tri-gas breath tests are currently under development.
• Mixed SIBO: Involves the presence of two or more gas-producing microorganism types, such as both hydrogen and methane producers.

SIBO and the gut microbiome: how SIBO affects the gut

Colonisation of the small intestine by excess bacteria can disrupt normal processes in the body, including digestion and absorption. Bacteria can consume nutrients before the body has had a chance to absorb them. For example, they can feed directly on vitamin B12 and deconjugate bile salts that are essential for fat digestion, impairing absorption of fat-soluble vitamins A, D, E and K. This is known as malabsorption¹.

Bacteria can also prematurely ferment ingested carbohydrates, leading to the generation of hydrogen, methane and hydrogen sulfide gases that distend the intestinal lumen and impair motility¹. Over time, this dysbiosis can trigger mucosal inflammation that may damage the intestinal lining and compromise tight junctions between epithelial cells, sometimes described as increased intestinal permeability. This can allow bacterial toxins and undigested food particles to pass into the bloodstream, triggering localised and systemic inflammation⁶.

Common symptoms of SIBO

SIBO is more commonly reported in people with underlying digestive conditions, particularly irritable bowel syndrome (IBS), with studies finding SIBO in 4–20% of IBS cases based on lactulose breath testing⁷. SIBO can cause both gastrointestinal and systemic symptoms, and these often overlap with other gut disorders such as IBS. The most commonly reported gastrointestinal symptoms include^1,5:

• Bloating and abdominal swelling.
• Diarrhoea.
• Abdominal pain and cramping.
• Gas.
• Nausea.
• Weight loss.

Other symptoms that do not directly involve the gastrointestinal system may include fatigue, food intolerances and brain fog, which is thought to be linked to dysregulation of the gut–brain axis. Different types of SIBO may cause different but overlapping symptoms. For example, hydrogen-dominant SIBO may cause gas, diarrhoea, bloating and abdominal pain, while IMO is commonly associated with constipation, bloating and belching.

Current approaches to SIBO management

The main goals of current SIBO treatment are to eradicate excess microorganisms from the small intestine, reduce symptoms, maintain remission, prevent recurrence and correct any nutritional or vitamin deficits¹. Current approaches include:

• Antibiotic therapy: Antibiotics are the primary treatment for SIBO. Rifaximin is commonly used as first-line therapy, while rifaximin combined with neomycin is often used for IMO. However, recurrence after antibiotic treatment is common¹.
• Dietary approaches: Dietary strategies such as a low FODMAP diet may help reduce symptoms by limiting fermentable carbohydrates. Restrictive diets should only be used short term, usually no longer than six weeks, and if ineffective they should not be repeated. Elemental diets have shown potential benefits. In one study involving patients with SIBO treated with an elemental diet for 14 days, the overall symptomatic response rate was 85%, as indicated by normalisation of breath tests^8,9.
• Addressing underlying causes: Treating SIBO often requires identifying and managing factors that contribute to bacterial overgrowth. SIBO is more common in people with IBS and other conditions, including chronic pancreatitis, diabetes, coeliac disease, Crohn’s disease, possible chronic proton pump inhibitor (PPI) use, or previous gastrointestinal surgery^4,5.
• Supporting gut motility: Impaired gut motility contributes to bacterial overgrowth in the small intestine. Prokinetic agents may help support the migrating motor complex (MMC) and reduce recurrence risk after antibiotic treatment. In one clinical study, patients who took PPIs plus prokinetics reduced their risk of SIBO compared with patients who received PPIs alone¹⁰.

Probiotics for SIBO: what does the evidence show?

Probiotics have gained attention as a potential support for SIBO, especially to address the limitations of antibiotic therapy, such as recurrence, antibiotic resistance and disruption of beneficial microbiota. While there is no single “best probiotic for SIBO”, some studies have explored specific strains.

Bacillus coagulans

In a pilot study, Bacillus coagulans was investigated after antibiotic treatment in SIBO patients over six months. The probiotic group achieved a negative breath test in 93.3% of cases compared with 66.7% in the antibiotic-only group, with significant reductions in diarrhoea, abdominal pain, gas and bloating¹¹.

Saccharomyces boulardii

A clinical study in patients with systemic sclerosis and SIBO found that Saccharomyces boulardii alone achieved 33% SIBO eradication, rising to 55% when used in combination with metronidazole, compared with 25% for metronidazole alone. Reductions in bloating, abdominal burning and diarrhoea were also reported¹².

In a clinical study involving patients with cirrhosis and SIBO, Saccharomyces boulardii led to eradication of SIBO in 80% of patients receiving probiotic treatment, compared with 23.1% in the placebo group¹³.

Bifidobacterium

A clinical study involving colorectal cancer patients with SIBO found that 81% of patients who received Bifidobacterium capsules tested negative on breath testing, compared with 25% in the placebo group¹⁴.

Lactobacillus strains and multi-strain probiotics

A clinical study in paediatric SIBO patients found that combining Lactobacillus rhamnosus with antibiotic therapy achieved partial or complete symptom resolution in 81.2% of children, compared with 67.7% in those receiving antibiotics alone¹⁵.

A clinical trial administered a four-strain probiotic containing Saccharomyces boulardii, Bifidobacterium lactis, Lactobacillus acidophilus and Lactobacillus plantarum to IBS patients with confirmed SIBO. A 71.3% decrease in total IBS symptom scores was observed in SIBO-positive patients after 30 days, compared with only 10.6% in those without SIBO, suggesting that probiotic benefit was greatest in the presence of bacterial overgrowth¹⁶.

It is important to note that not all probiotics are equally effective, and some may worsen symptoms in certain people¹. One study found that probiotic use in SIBO patients exacerbated bloating, flatulence and brain fog, with symptoms resolving only after the probiotic was discontinued and antibiotic therapy was initiated^1,17. There is also evidence that one month of probiotic use may predispose some patients to IMO¹.

So, can probiotics help SIBO? At present, there is no clear clinical consensus on whether probiotics are beneficial for treating SIBO or whether they may worsen it in some cases.

The gut microbiome after SIBO treatment

Following antibiotic treatment for SIBO, bacterial overgrowth may be reduced, but this can also temporarily disrupt the broader balance of the gut microbiome. While symptoms may improve, antibiotic therapy may deplete beneficial bacteria and reduce microbial diversity.

Nutrition can play an important role in supporting recovery of microbial diversity. A varied, nutrient-dense diet that includes fibre-rich foods may help support microbial diversity over time by providing fuel for beneficial bacterial regrowth¹⁸.

Clinical takeaways

SIBO is a relatively common condition that is often linked to underlying health issues. Antibiotics are typically used as first-line treatment, but recurrence is common, and concerns about microbiome disruption mean that other supportive approaches may also be considered. A fibre-rich, varied diet may help support microbial diversity and gut health after SIBO treatment.

Probiotics for SIBO should be considered carefully on an individual basis. Some strains, including Saccharomyces boulardii, Bacillus coagulans and certain Lactobacillus species, may be beneficial for some people, but probiotics may worsen symptoms for others¹.

References

1. Skrzydło-Radomańska B, Cukrowska B. How to recognise and treat small intestinal bacterial overgrowth? J Clin Med. 2022;11(20):6017.
2. Lewis S. Small bowel bacterial overgrowth in subjects living in residential care homes. Age Ageing. 1999;28(2):181–5.
3. Sorathia SJ, Chippa V, Rivas JM. Small intestinal bacterial overgrowth. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2026.
4. Rao SSC, Bhagatwala J. Small intestinal bacterial overgrowth: clinical features and therapeutic management. Clin Transl Gastroenterol. 2019;10(10):e00078.
5. Barlow GM, Pimentel M. Modern concepts of small intestinal bacterial overgrowth. Curr Opin Gastroenterol. 2025;41(6):399–408.
6. Wang Z, Tan W, Wu L, Zhang P, Xiong H, Zhu L, et al. Bacteroides, metabolites and lymphocytes: a triad of biomarkers in small intestinal bacterial overgrowth. Food Sci Nutr. 2025;13(6):e70367.
7. Šuran J, Pavlović N, Božić J, Kumrić M, Vukojević K, Filipović N, et al. IBS and SIBO: gut microbiota, pathophysiology and non-pharmacological interventions. Antibiotics. 2026;15(3):251.
8. Pimentel M, Constantino T, Kong Y, Bajwa M, Rezaei A, Park S. A 14-day elemental diet is highly effective in normalising the lactulose breath test. Dig Dis Sci. 2004;49(1):73–7.
9. Achufusi TGO, Sharma A, Zamora EA, Manocha D. Small intestinal bacterial overgrowth: comprehensive review of diagnosis, prevention and treatment methods. Cureus. 2020;12(6):e8860.
10. Revaiah PC, Kochhar R, Rana SV, Berry N, Ashat M, Dhaka N, et al. Risk of small intestinal bacterial overgrowth in patients receiving proton pump inhibitors versus proton pump inhibitors plus prokinetics. JGH Open. 2018;2(2):47–53.
11. Khalighi AR, Khalighi MR, Behdani R, Jamali J, Khosravi A, Kouhestani S, et al. Evaluating the efficacy of probiotic treatment in patients with small intestinal bacterial overgrowth: a pilot study. Indian J Med Res. 2014;140(5):604–8.
12. García-Collinot G, Madrigal-Santillán EO, Martínez-Bencomo MA, Carranza-Muleiro RA, Jara LJ, Vera-Lastra O, et al. Effectiveness of Saccharomyces boulardii and metronidazole for small intestinal bacterial overgrowth in systemic sclerosis. Dig Dis Sci. 2020;65(4):1134–43.
13. Efremova I, Maslennikov R, Zharkova M, Poluektova E, Benuni N, Kotusov A, et al. Efficacy and safety of a probiotic containing Saccharomyces boulardii CNCM I-745 in the treatment of small intestinal bacterial overgrowth in decompensated cirrhosis: randomised, placebo-controlled study. J Clin Med. 2024;13(3):919.
14. Liang S, Xu L, Zhang D, Wu Z. Effect of probiotics on small intestinal bacterial overgrowth in patients with gastric and colorectal cancer. Turk J Gastroenterol. 2016;27(3):227–32.
15. Peinado Fabregat MI, Gardner RM, Hassan MA, Kapphahn K, Yeh AM. Small intestinal bacterial overgrowth in children: clinical features and treatment response. JPGN Rep. 2022;3(2):e185.
16. Leventogiannis K, Gkolfakis P, Spithakis G, Tsatali A, Pistiki A, Sioulas A, et al. Effect of a preparation of four probiotics on symptoms of patients with irritable bowel syndrome: association with intestinal bacterial overgrowth. Probiotics Antimicrob Proteins. 2019;11(2):627–34.
17. Rao SSC, Rehman A, Yu S, De Andino NM. Brain fogginess, gas and bloating: a link between SIBO, probiotics and metabolic acidosis. Clin Transl Gastroenterol. 2018;9(6):e162.
18. Penumutchu S, Korry BJ, Hewlett K, Belenky P. Fibre supplementation protects from antibiotic-induced gut microbiome dysbiosis by modulating gut redox potential. Nat Commun. 2023;14(1):5161.