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Saccharomyces Boulardii: The Complete Guide (2022)

Researched and Written by:
Bailey Franzen MS, RDN Bailey Franzen MS, RDN

If you've heard about S Boulardii, but feel a bit confused, this guide will clear up everything.  You'll learn what it does, how it helps and how much to take based on studies.

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Table of Contents

    What Is Saccharomyces Boulardii?

      Saccharomyces boulardii is a probiotic yeast that was discovered in 1923 by a French microbiologist, Henri Boulard, while in IndoChina (Southeast Asia) searching for new strains of yeast that could be used in the fermenting process.1,2,3

      Boulard happened to be visiting during a cholera outbreak and noticed that people who did not develop cholera were drinking a special tea.1   The tea was made by cooking down the outer skins from the tropical fruits, lychee and mangosteens.1

      Lychee Mangosteen S Boulardii

      Boulard was successful in identifying the responsible cholera-preventing agent, which was a special strain of yeast he then named “Saccharomyces boulardii.”

      Today, the probiotic yeast, S. boulardii, is widely used in the food and nutraceutical industries, and has been used as a probiotic for >50 years.2,4 

      Probiotics are defined as, “live microorganisms which when administered in adequate amounts confer a health benefit to the host.” 5 

      While bacteria typically dominate the probiotic scene, the yeast S. boulardii is a probiotic force to be reckoned with.

      1. S. boulardii is known to be effective for limiting diarrheal issue, and has been shown to work in opposition to several gut pathogens through anti-toxin and antimicrobial actions.1,2
      2. S. boulardii has both prebiotic and probiotic properties and has been shown to support intestinal barrier integrity.6 
      3. S. boulardii also helps to rapidly reestablish a normal microbiota after the shock of antibiotics, enhances the production of beneficial microbial byproducts (e.g. SCFAs, and polyamines), and has demonstrated immune system regulating properties.1
      4. In fact, S. boulardii is currently the only yeast probiotic that has been proven effective in double-blind studies, even outperforming common probiotics such as Bifidobacterium and Lactobacillus in immune system regulation (immunomodulation).2 

      While S. boulardii offers multiple benefits, this probiotic yeast is not commonly found in our diet or in fermented foods.

      Likewise, S. boulardii is not a natural colonizer of the human GI tract, meaning that it’s not already present in our guts and capable of being stimulated by factors such as prebiotics.3

      This means that S. boulardii must be derived from supplements to experience consistent exposure to this beneficial yeast.

      Saccharomyces Boulardii vs Saccharomyces Cerevisiae (aka Brewer's Yeast)

      So what's the difference between Saccharomyces Boulardii and Saccharomyces Cerevisiae (aka Brewer’s Yeast)?

    • Well, S. boulardii is a yeast strain categorized under the yeast species of Saccharomyces cerevisiae.4 In general, the species S. cerevisiae is commonly associated with fermentation processes like winemaking, baking, and brewing.
    • While S. boulardii is genetically very similar to S. cerevisiae (brewer’s yeast) there are some key differences that set S. boulardii apart from more commonly encountered yeast strains often used for fermentation.
      1. To begin, animal model studies suggest that other strains of S. cerevisiae are rapidly cleared from the body in less than a day potentially limiting their beneficial health effects.1   And now, while S. boulardii does not colonize the human GI tract after supplementation, it has a much slower clearance rate, achieving a steady-state concentration after 3 days of supplementation and hanging around for upwards of 3-5 days after supplementation is discontinued.7
      2. S. boulardii differs from other strains of S. cerevisiae  in that it prefers growth temperatures that are the norm in the human body (37°C).1
      3. S. boulardii is also resistant to the acidic pH of the human stomach and is tolerant of bile acids; whereas other strains of S. cerevisiae prefer cooler temperatures (30-33°C) and do not survive well in acidic pH ranges.1 Because of these physiological advantages, S. boulardii is known to have a faster growth rate in the intestinal tract than S. cerevisiae.4 

      The bottom line: S. boulardii has multiple benefits above and beyond those found in more commonly ingested strains of yeast.

      These benefits are facilitated by its ability to cope with the physiological obstacles of the human body such as body temperature and stomach acidity.1 

      Saccharomyces Boulardii vs 'Normal' Probiotics

      Compared to bacteria-based probiotics (e.g. Lactobacillus, Bifidobacterium, etc.) S. boulardii has the advantage of being naturally resistant to all antibiotics due to being a yeast.4

      In fact S. boulardii is commonly used alongside antibiotics for the prevention of antibiotic associated diarrhea, helping to stabilize the gut ecosystem and restore microbiome normalcy more rapidly.7,8 

      Additionally, a common concern about bacterial probiotics is the risk of probiotics sharing and acquiring antibiotic resistance genes with other microbes, which could potentially be passed on to pathogenic bacteria, possibly rendering antibiotics ineffective during an infection.

      S. boulardii is incapable of acquiring or sharing antibiotic-resistant genes due to it being a type of yeast and not a form of bacteria, meaning that it poses no risks of contributing to antibiotic resistance in bacteria.1,3,9 

      How Does S Boulardii Work?

    • S. boulardii has several mechanisms of action which confer benefit and are broken down into three broad categories:1 
      1. Interaction with the microbiome and potential pathogens in the gut.  (Luminal action)
      2. Promoting health and integrity of the gut lining.  (Trophic action)
      3. Regulating Immune Responses.  (Mucosal action)

      To be honest, this all gets really complex - so if you want to geek out with us, we've written a separate article on exactly how Saccharomyces Boulardii works, which you can find here.

      And of course, if you just want to see the potential benefits of Saccharomyces Boulardii at a glance, here they are...

      General Summary of  S. boulardii Actions: 

      • Preservation of the protective mucus layer
      • Support elimination of bacterial toxins 
      • May bind to pathogens to protect against ill-effects
      • Delivers a prebiotic action
      • Can promote regeneration of intestinal (mucosal) cells 
      • Can help stimulation of digestive enzymes (through brush border activity) 
      • Regeneration and stabilization of the healthy microbiota
      • General healthy immune stimulation and regulation 
      • Anti Inflammatory action
      • Anti-secretory action (anti-diarrheal; reduces water and electrolyte losses)3  

      Who Can S Boulardii Help?

      S boulardii has been used in relation to several gastrointestinal issues, including: antibiotic-associated diarrhea, acute diarrhea, persistent diarrhea, enteral nutrition-related diarrhea, traveler’s diarrhea, Helicobacter pylori, as well as more serious issues.7

      In this section, we'll focus on how S Boulardii can help with diarrhea, since that is our major focus.

      Traveler's Diarrhea

      • Travelers' diarrhea affects 20–60% of travelers to regions of the world.37 

      • A meta-analysis of 12 randomized controlled trials of various probiotics (including S. boulardii) for the prevention of traveler’s diarrhea found a significant reduction in the risk of traveler’s diarrhea when probiotics are used.7 

      • Studies evaluating S. boulardii for the prevention of travelers' diarrhea found a reduction between 5% and 11%.7 

      • Effective doses for the prevention of traveler’s diarrhea are 250-1000 mg per day in adults taken over the duration of the trip (3 weeks).1 

      Antibiotic-associated diarrhea (AAD)

      • AAD is diarrhea that is otherwise unexplained that occurs after taking antibiotics.7 
      • A review article which analyzed data from multiple studies and a total of 4,780 study participants, looked at the administration of S. boulardii for the treatment of AAD. 
      • The study found that S. boulardii reduced the risk of AAD compared to placebo. For adults, the risk of developing AAD was 17.4% which decreased down to 8.2% when taking S. boulardii. In children, S. boulardii reduced the risk from 20.9% to 8.8%.8   
      • The optimal dose of probiotics, including S. boulardii, has not been established for AAD. Various doses of S. boulardii were used with no clear dose‐dependent effect.
      • Until more data on the optimal dose of S. boulardii become available, a daily dose of not less than 250 mg but not more than 500 mg in children and not more than 1000 mg in adults could be used to match the doses used in RCTs for the treatment of AAD.8 
      • To match clinical trials showing a clear benefit, S. boulardii administration should be started early in the course of antibiotic treatment before alteration of the gut flora and overgrowth of pathogens occurs.8
      • Based on the published trials, it seems appropriate to continue the administration of S. boulardii for the duration of antibiotic treatment. Whether longer administration is necessary is not clear, as S. boulardii was administered after cessation of antibiotic therapy in only two RCTs with no clear benefit.

      On the other hand, as diarrhea may occur up to several months following cessation of such treatment, some cases of AAD may have been missed.8

      Acute Diarrhea in Children and Adults

      • Twenty-nine randomized controlled trials evaluated the ability of S. boulardii to reduce the duration of acute diarrhea in children. S. boulardii use was also associated with a reduced duration of hospitalization.36 
      • S. boulardii reduced the risk of diarrhea on day 2 to day 7 suggesting that S. boulardii provides benefit for several diarrheal outcomes.36
      • Additionally, studies using S. boulardii showed that this probiotic may be effective in treating acute adult diarrhea due to a variety of causes and can significantly lower diarrhea severity scores compared with controls.7 
      • Effective adult dosages typically range from 500-750 mg/day for acute diarrhea, with administration lasting 8-10 days.1 
      • The most commonly administered daily dose of S. boulardii for acute diarrhea in children is 500 mg. The duration of the intervention typically lasted 5 days; however, intervention duration has been studied for acute diarrhea for time periods between 3-10 days.36
      • Administration should begin within 72 hours after the initial onset of acute diarrhea.36

      Persistent diarrhea

      • Results from clinical trials indicate that S. boulardii improves outcomes in children with persistent (chronic) diarrhea. 
      • Compared to controls, individuals in the S. boulardii administration groups experience a 50% reduction in persistent diarrhea symptoms. This suggests that S. boulardii is useful in the management of persistent diarrhea in children. However, studies with larger populations are needed.7 
        • Side note:  We tried to look up dosing on this with no such luck. One study administered the probiotic in a milk based beverage, but the amount administered wasn’t entirely clear -- basically it was like 1010- 1012 CFU per gram of powder, but not clear on how many grams were administered as part of the beverage.
        • The weight of the milk/powder appeared to be included in the reported 175 gram dose twice daily; an amount which would be insane/impractical for the probiotic alone, hence no dosing info for this). 

      How Much S Boulardii? (Dosing & Duration)

      • Multiple doses and durations of S. boulardii administration have been studied for a variety of conditions with successful outcomes.1 
      • Dosing of S. boulardii for common uses is often set by a weight dosage measured in milligrams or grams, or by a number of colony forming units (CFUs). 
      • Commonly administered CFU dosing is 2-5 billion CFUs (2–5 × 109).44 
      • Common dosages in milligrams vary by disease state, but most often range from 500-1000 mg for adults and 250-500 mg for children.  

      How Long Does It Take To Work & How Long Does It Last?

      Duration of supplementation has been studied for as little as 3 days or up to 6 months depending on the disease state being treated. 

      S. boulardii, when given by mouth, achieves a steady-state concentration in the gut within three days and is cleared within 3-5 days after it is discontinued.1 

      Total SCFA concentrations remain elevated 9-10 days after S. boulardii discontinuation which suggests a prolonged action of the yeast, and indicates that daily treatment may not be necessary to sustain its effects on SCFA concentrations.14

      However, it is important to note that S. boulardii does not colonize the human gut, meaning that while daily supplementation may not be necessary to reap benefits, continued supplementation is still necessary to continue experiencing benefits of this probiotic yeast.44 

      Issue

      Dose (mg/day)

      Duration

      Strength of Evidence *

      Antibiotic Associated Diarrhea (Prevention)

      500-1000 (adults)

      250-500 (children)

      During Antibiotic Administration and up to 3 days to 2 weeks after

      ++++

      Traveler’s Diarrhea (Prevention) 

      250-1000 (adults)

      Duration of trip (3 weeks) 

      +++

      Tube-feeding related diarrhea

      2000  (adults)

      8-28 days

      ++

      Acute Diarrhea

      500-750 (adults)

      500 (children)

      8-10 days

      +

       

      *Strength of evidence: + (weak; needs more randomized controlled trials) to ++++ (strong, efficacy and safety are evidence based from numerous large randomized controlled trials).

      Table adapted from:1,8,36,40  

      When & How Should You Take It?

      S. boulardii can be taken with or without food at any time of day.

      One study found that taking S. boulardii along with the fiber, psyllium, helps to increase the concentration of S. boulardii in the gut by 22%, but this same effect was not seen with other fiber types such as pectin.1

      S. boulardii should not be taken with antifungal medications, or be taken by severely immunocompromised individuals without physician oversight or approval.46

      Consult a physician before taking S. boulardii along with any prescribed or over the counter medications and supplements.

      What To Look For In A S Boulardii Supplement?

      How a probiotic product is manufactured may significantly affect its potency over time (shelf-life).

      S. boulardii is usually available in capsules of either lyophilized (freeze-dried) or heat-dried preparations.1

      • Heat-dried products require refrigeration after opening and lose their potency rapidly. You can spot heat-dried S. boulardii if/when the product packaging states that the product requires refrigeration.1
      • Lyophilized preparations of S. boulardii are stable over one year at room temperature, as long as it is protected from moisture, and do not require refrigeration.1 
      • Lyophilized products have the advantage of portability and convenience and maintain high viability counts over prolonged periods. A study of four S. boulardii products in Germany found a lyophilized product outperformed three heat-killed S. boulardii preparations in terms of higher viable cells and quicker start-up times.1 

      Even if a product label states it contains S. boulardii, a variation in effectiveness may occur if the company has supplied a product with a lower than stated dose or inaccurate strain composition of S. boulardii.1

      For instance, four S. boulardii products were tested  in Brazil, only two of which (50%) were protective in a Salmonella typhimurium mouse model study. The remaining two S. boulardii products were ineffective.1

      Although most products state they contain at least 1 × 109 S. boulardii/mg, independent tests have determined 50% of the products contained a dose less than on the label. In one study comparing six S. boulardii products, only 50%  had the same concentration identified on their label.1

      Without access to specific quality control tests for commercially available probiotic products, the choice of a high quality product can be difficult.We suggest purchasing S. boulardii from a GMP certified facility, and through a company who can readily supply independent third party testing results. 

      Safety

      Although the use of S. boulardii is considered safe, yeast infections (fungemia) have been observed in critically ill and/or immunocompromised patients.3

      However, the safety of S. boulardii has been proven in numerous clinical investigations in healthy as well as severely ill patients. The risk of developing fungemia due to the intake of S. boulardii is estimated to be 1 out of 5.6 million users. The reported cases of fungemia associated with S. boulardii intake were in extremely ill patients, either immunocompromised or with central venous catheters.

      For all other groups, the intake of S. boulardii is considered to be safe.4  

      Since Saccharomyces boulardii is a yeast, people with yeast allergies are advised to avoid its use.45

      Our Summary

      S. boulardii is a beneficial probiotic yeast that has been widely used for > 50 years.

      It may support the following functions...

      1. Helps in the prevention, treatment, and recovery of a number of diarrheal issues
      2. Has anti-toxin and anti-pathogen effects
      3. Increases beneficial metabolites in the gut (polyamines, SCFAs)
      4. Helps to improve gut barrier integrity 
      5. Improves microbiome balance in the setting of dysbiosis. 
      6. Induces general immune stimulation and regulation 
      7. May work as both a prebiotic and probiotic at the same time
      8. Has antiinflammatory action
      9. Stimulates the production of digestive enzymes

      Commonly administered doses are 2-5 billion CFUs or dosing by milligrams of 500-1000 mg for adults, and 250-500 mg for children, though dosing varies by disease state.

      Studied durations of treatment range from 3-6 months, with intervention duration varying based on disease state.

      S. boulardii reaches peak gut concentrations after 3 days of use, and is no longer detectable after 3-5 days post-discontinuation; however, beneficial impacts on gut metabolites (SCFAs) have been noted even 9-10 days after supplementation stops. 

      S. boulardii is not a natural colonizer of the GI tract, meaning continued supplementation is necessary to receive benefit, though daily use may not be necessary to achieve a beneficial effect.

        Evidence Based

        An evidence hierarchy is followed to ensure conclusions are formed off of the most up-to-date and well-designed studies available. We aim to reference studies conducted within the past five years when possible.

        • Systematic review or meta-analysis of randomized controlled trials
        • Randomized controlled trials
        • Controlled trials without randomization
        • Case-control (retrospective) and cohort (prospective) studies
        • A systematic review of descriptive, qualitative, or mixed-method studies
        • A single descriptive, qualitative, or mixed-method study
        • Studies without controls, case reports, and case series
        • Animal research
        • In vitro research

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