An unsung hero – Saccharomyces Boulardii

An unsung hero – Saccharomyces Boulardii

Saccharomyces Boulardii is a probiotic that many find as difficult to pronounce as ‘supercalifragilisticexpialidocious’, so it often gets the shortened version of S. Boulardii. Saccharomyces Boulardii (pronounced SAK-a-ROE-mye-SEES boo-LAR-dee-eye), or S.Boulardii is not just one of the oldest strains of probiotics it is also one of the most studied. It has certainly stood the test of time as a way to help support and maintain gut health.

The origins

It was first discovered in 1923 by Henri Boulard, who was a French microbiologist. He isolated and identified Saccharomyces Boulardii as a yeast strain probiotic after he observed natives of Southeast Asia chewing on the skins of lychees and mangosteens to treat diarrhoea during a cholera epidemic.[i] S.Boulardii. is a probiotic and is a strain of saccharomyces cerevisiae which are species related to brewer’s yeast but not related to the yeast group such as Candida. It has been used for decades to help support a healthy digestive system and importantly, it has been extensively studied for its potential benefits on human health.

What does Saccharomyces Boulardii do?

S.Boulardii is a non-colonising, transient yeast which means it passes through for a short time and does not take up residence in the human gastrointestinal tract (GI ).  Instead, it has shown to influence the existing microbiome present in the GI tract before it finally makes its way out of the body.

One of the main obstacles for most probiotics is the very acidic environment of the stomach and the presence of pepsin, an enzyme designed for protein breakdown and to inhibit microorganisms. Therefore, probiotics must be designed specifically to survive this unfriendly landscape they find themselves in to enable sufficient numbers to reach the GI tract. However, S.Boulardii remains viable after being exposed to gastric juices, pepsin and hydrochloric acid.[ii]

During its transition through the digestive tract, S.Boulardii helps to support a healthy balance of our microbiome as it promotes the growth of the beneficial bacteria therefore balancing intestinal microbial homeostasis . It has also been shown to inhibit the growth of other harmful species.

Clinical uses of Saccharomyces Boulardii

S.Boulardii is best known for its ability to relieve the symptoms of diarrhoea which was the original finding by Henry Boulard. There are multiple etiologies of acute and persistent diarrhoea such as –

  • Antibiotic associated diarrhoea (AAD).
  • IBS-D – loose watery stools associated with irritable bowel syndrome.
  • Travelling
  • Viruses.
  • Gastro Intestinal infections.
  • Side effects from some medications.
  • Runners who experience frequent, loose bowels during or immediately after a run.
  • Inflammatory bowel disease (IBD).
  • Malabsorption.

When taking antibiotics, probiotics are generally not advised to be used at the same time as there are increased risks that the antibiotic can affect the probiotic organisms, taking them following a course can be very beneficial. However, S.boulardii is a yeast and therefore naturally resistant to antibiotics so they can be taken at the same time to lessen the known side-effects such as diarrhoea.

Clostridium difficile (C.Diff) is a bacterium that can develop when taking antibiotics or once a course has finished which can cause cramps, nausea, watery, sometimes bloody diarrhoea.[iii] Of the many probiotics researched, S.Boulardii has been shown to have powerful effects by inhibiting the C.Diff pathogenic bacteria and their toxic byproducts which trigger the loose, watery stools.

It has also been tested for its clinical efficacy with other types of GI infections including parasitic infections such as blastocystis hominis and giardiasis as well as bacterial infections particularly Helicobacter pylori. Whilst is a yeast strain it can limit the growth of unwanted opportunistic yeasts in the gut such as candida albicans by inhibiting its adhesion.[iv]


S.Boulardii’s many actions in the GI tract are impressive, from supporting the production of secretory IgA (SIgA) which is an immunoglobulin that acts as a first line of defence at all mucosal surfaces, helping to modulate our immune system responses. Both the innate and adaptive immune responses are supported by the actions of S.Boulardii[v]

Our GI tract is home for a vast number of microbes that have many roles to play in our overall health, especially locally in the gut, the regulation of inflammation is one major function. The number of individuals living with Inflammatory bowel diseases (IBD) has increased dramatically, with 1 in every 123 people are living with Crohn’s or Colitis, and this number rises to 1 in every 67 individuals in their 70’s.[vi]  

In small studies those with Crohn’s disease treated with S.Boulardii had significant improvement and were found to have a reduction in colonic permeability compared to those who had been prescribed a placebo drug.[vii] It shows promise for IBD and IBS due to its immunomodulatory , anti-inflammatory and antimicrobial effects.

Whilst S.Boulardii may not have been so widely known as other probiotics, it can stand as proud as other well known strains, with its own unique benefits and potential applications in managing a wide range of gastrointestinal complaints.



[ii] Pais P, Almeida V, Yılmaz M, Teixeira MC. Saccharomyces boulardii: What Makes It Tick as Successful Probiotic? J Fungi (Basel). 2020 Jun 4;6(2):78. doi: 10.3390/jof6020078. PMID: 32512834; PMCID: PMC7344949.


[iv] Murzyn A, Krasowska A, Augustyniak D, Majkowska-Skrobek G, Łukaszewicz M, Dziadkowiec D. The effect of Saccharomyces boulardii on Candida albicans-infected human intestinal cell lines Caco-2 and Intestin 407. FEMS Microbiol Lett. 2010 Sep 1;310(1):17-23. doi: 10.1111/j.1574-6968.2010.02037.x. Epub 2010 Jun 16. PMID: 20629753.

[v] Kelesidis T, Pothoulakis C. Efficacy and safety of the probiotic Saccharomyces boulardii for the prevention and therapy of gastrointestinal disorders. Therap Adv Gastroenterol. 2012 Mar;5(2):111-25. doi: 10.1177/1756283X11428502. PMID: 22423260; PMCID: PMC3296087.


[vii] Kelesidis T, Pothoulakis C. Efficacy and safety of the probiotic Saccharomyces boulardii for the prevention and therapy of gastrointestinal disorders. Therap Adv Gastroenterol. 2012 Mar;5(2):111-25. doi: 10.1177/1756283X11428502. PMID: 22423260; PMCID: PMC3296087.

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Elisabeth Philipps

Karen Devine

Karen Devine

Shelley Harvey

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