See also: Saccharomyces (genus page)
Saccharomyces boulardii is a non-pathogenic yeast strain used as a probiotic across a wide range of gastrointestinal and inflammatory conditions.
Taxonomically a strain of S. cerevisiae, it is phenotypically distinct—optimally active at 37°C (human body temperature), acid-resistant, and a transient colonizer that does not permanently establish in the gut.
It is the most studied probiotic fungus and the only yeast with substantial clinical trial evidence across multiple disease contexts.
Evidence map8 cited passagesInspect provenance +
An RCT demonstrated that S. boulardii supplementation in MS patients modulated gut microbiome composition and immune markers. This is notable as one of the few fungal probiotic trials in neuroinflammatory disease.
Meta-analysis evidence supports S. boulardii for maintaining remission in ulcerative colitis and Crohn's disease, with particular efficacy in preventing C. difficile-associated relapse.
Meta-analysis of probiotics for NEC prevention in VLBW infants includes S. boulardii as a component of effective probiotic combinations.
Discussed in reviews of probiotics for ASD via the gut-brain axis, though species-specific ASD trial data for S. boulardii alone is limited.
Part of the gut mycobiome discussion in CKD, where fungal dysbiosis affects immunological profiles.
Discussed in cardiometabolic disease mycobiome studies.
Relevant to cancer mycobiome interventions.
Altered in gestational diabetes mycobiome.
Mechanism of Action#
S. boulardii exerts probiotic effects through multiple mechanisms. Pathogen exclusion: Competes with pathogenic bacteria and fungi for adhesion sites and nutrients. Toxin neutralization: Produces proteases that degrade Clostridioides difficile toxins A and B.
Anti-inflammatory signaling: Modulates NF-kB, reduces pro-inflammatory cytokine production (TNF-alpha, IL-6, IL-8), and enhances anti-inflammatory IL-10.
Barrier protection: Stimulates secretory IgA production and enhances tight junction integrity. SCFA modulation: Increases Butyrate-producing bacterial populations indirectly.
Clinical Evidence by Condition#
Multiple Sclerosis#
An RCT demonstrated that S. boulardii supplementation in MS patients modulated Gut Microbiome composition and immune markers.[1]Motlagh Asghari 2023 — Saccharomyces boulardii probiotic supplementation in multiple sclerosis: 4-month randomized clinical trialKimia Motlagh Asghari, Neda Dolatkhah, Hormoz Ayromlou et al. · 2023Open reference 1 ↓ This is notable as one of the few fungal probiotic trials in neuroinflammatory disease.
Inflammatory Bowel Disease#
Meta-analysis evidence supports S. boulardii for maintaining remission in ulcerative colitis and Crohn's disease, with particular efficacy in preventing C. difficile-associated relapse.[2]Effect of Probiotics on Inducing Remission and Maintaining Therapy in Ulcerative Colitis, Crohn's Disease, and Pouchitis: Meta-analysis of Randomized Controlled TrialsShen J, Zuo ZX, Mao AP · 2014Open reference 2 ↓[3]Mabrouk 2026 -- Repurposing Gut Microbiota Modulators: Insights into Current and Novel ApplicationsReda R. Mabrouk, Amani Magdy Beshbishy, Waad Mohamed Elmalah et al. · 2026Open reference 3 ↓
Necrotizing Enterocolitis#
Meta-analysis of probiotics for NEC prevention in VLBW infants includes S. boulardii as a component of effective probiotic combinations.[4]Zhou 2023 — Probiotics Prevent NEC in VLBW (Network Meta-Analysis)Zhou et al. · 2023Open reference 4 ↓
Autism Spectrum Disorder#
Discussed in reviews of probiotics for ASD via the gut-brain axis, though species-specific ASD trial data for S. boulardii alone is limited.[5]Feng 2023 — Probiotics in Treatment of ASD: Gut-Brain Axis PerspectivesPengya Feng, Shuai Zhao, Yangyang Zhang et al. · 2023Open reference 5 ↓
Mycobiome Context#
Part of the gut mycobiome discussion in CKD, where fungal Dysbiosis affects immunological profiles.[6]Gut Mycobiome in Patients with CKD Was Altered and Associated with Immunological ProfilesJialin Hu, Shichao Wei, Yifeng Gu et al. · 2022Open reference 6 ↓ Discussed in cardiometabolic disease mycobiome studies.[7]Gut mycobiome in cardiometabolic disease progression: current evidence and future directionsXiaoyu Wei, Zixin Guo, Jingyang Wang et al. · 2025Open reference 7 ↓[8]Gut Mycobiome in Cardiometabolic Disease Progression: Current Evidence and Future DirectionsXiaoyu Wei, Zixin Guo, Jingyang Wang et al. · 2025Open reference 8 ↓
Relevant to cancer mycobiome interventions.[9]The mycobiome in human cancer: analytical challenges, molecular mechanisms, and therapeutic implicationsTing Ding, Chang Liu, Zhengyu Li · 2025Open reference 9 ↓ Altered in gestational diabetes mycobiome.[10]Wang 2026 — Intestinal Fungal Dysbiosis in Gestational Diabetes Mellitus Associated with Adverse Pregnancy OutcomesWenxin Wang, Sha Lu, Yuanqing Fu et al. · 2026Open reference 10 ↓
Cross-References#
- Saccharomyces—genus page
- Mycobiome—fungal component of gut microbiome
- Candida albicans—pathogenic fungus that S. boulardii competitively excludes
- dysbiosis—S. boulardii as mycobiome-modulating intervention
- Interleukin-6 (IL-6)—S. boulardii reduces IL-6 production
References 11
Numbered by first appearance in the article, then reconciled with its declared source list.
- 1
Kimia Motlagh Asghari, Neda Dolatkhah, Hormoz Ayromlou et al. (2023). Motlagh Asghari 2023 — Saccharomyces boulardii probiotic supplementation in multiple sclerosis: 4-month randomized clinical trial. Scientific Reports.
- 2
Shen J, Zuo ZX, Mao AP (2014). Effect of Probiotics on Inducing Remission and Maintaining Therapy in Ulcerative Colitis, Crohn's Disease, and Pouchitis: Meta-analysis of Randomized Controlled Trials. Inflammatory Bowel Diseases.
- 3
Reda R. Mabrouk, Amani Magdy Beshbishy, Waad Mohamed Elmalah et al. (2026). Mabrouk 2026 -- Repurposing Gut Microbiota Modulators: Insights into Current and Novel Applications. Beni-Suef University Journal of Basic and Applied Sciences.
- 4
Zhou et al. (2023). Zhou 2023 — Probiotics Prevent NEC in VLBW (Network Meta-Analysis). Frontiers in Pediatrics.
- 5
Pengya Feng, Shuai Zhao, Yangyang Zhang et al. (2023). Feng 2023 — Probiotics in Treatment of ASD: Gut-Brain Axis Perspectives. Frontiers in Microbiology.
- 6
Jialin Hu, Shichao Wei, Yifeng Gu et al. (2022). Gut Mycobiome in Patients with CKD Was Altered and Associated with Immunological Profiles. Frontiers in Immunology.
- 7
Xiaoyu Wei, Zixin Guo, Jingyang Wang et al. (2025). Gut mycobiome in cardiometabolic disease progression: current evidence and future directions. Frontiers in Microbiology.
- 8
Xiaoyu Wei, Zixin Guo, Jingyang Wang et al. (2025). Gut Mycobiome in Cardiometabolic Disease Progression: Current Evidence and Future Directions. Frontiers in Microbiology.
- 9
Ting Ding, Chang Liu, Zhengyu Li (2025). The mycobiome in human cancer: analytical challenges, molecular mechanisms, and therapeutic implications. Molecular Cancer.
- 10
Wenxin Wang, Sha Lu, Yuanqing Fu et al. (2026). Wang 2026 — Intestinal Fungal Dysbiosis in Gestational Diabetes Mellitus Associated with Adverse Pregnancy Outcomes. BMC Pregnancy and Childbirth.
- 11
Magill RG, MacDonald SM (2023). Magill 2023 — Male Infertility and the Human Microbiome. Frontiers in Reproductive Health.
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