# Saccharomyces cerevisiae var. boulardii VSL

**Canonical URL:** https://ingredients.hermeticasuperfoods.com/ingredients/saccharomyces-cerevisiae-var-boulardii-vsl
**Data Source:** Hermetica Superfoods Ingredient Encyclopedia
**Updated:** 2026-04-03
**Evidence Score:** 2 / 10
**Category:** Fermented/Probiotic
**Also Known As:** S. cerevisiae var. boulardii VSL, Saccharomyces boulardii VSL strain, VSL probiotic yeast, S. boulardii VSL, Boulard's yeast VSL variant

## Overview

Saccharomyces cerevisiae var. boulardii VSL is a [probiotic](/ingredients/condition/gut-health) yeast strain that produces bioactive metabolites including capric acid and caprylic acid with demonstrated antifungal activity against Candida albicans in vitro. Its primary mechanisms involve disruption of fungal cell membranes, bile salt tolerance enabling gastrointestinal survival, and modulation of tryptophan catabolism pathways to influence immune signaling.

## Health Benefits

• Antifungal activity against Candida albicans through bioactive compounds (preliminary evidence from in vitro studies)
• Enhanced gut survival due to bile tolerance up to 2.5% and pH 4 resistance (preliminary in vitro evidence)
• Potential [immunomodulatory](/ingredients/condition/immune-support) effects via altered tryptophan catabolism pathways (preliminary genetic analysis)
• Thermotolerance at body temperature (37°C) for optimal gut colonization (preliminary laboratory evidence)
• Note: No human clinical trials specific to VSL strain were found in the research

## Mechanism of Action

Saccharomyces cerevisiae var. boulardii VSL exerts antifungal effects primarily through secreted bioactive lipid compounds, including medium-chain fatty acids such as capric acid, which disrupt Candida albicans cell membrane integrity by targeting phospholipid bilayer organization. The strain's resistance to bile concentrations up to 2.5% and low pH environments (pH 4) is attributed to membrane ergosterol composition and active proton pump activity, enabling colonization of the lower gastrointestinal tract. Additionally, the strain alters tryptophan catabolism by influencing indole pathway metabolites, which interact with aryl hydrocarbon receptors (AhR) on intestinal immune cells to modulate [cytokine](/ingredients/condition/inflammation) production and regulatory [T-cell](/ingredients/condition/immune-support) activity.

## Clinical Summary

Current evidence for Saccharomyces cerevisiae var. boulardii VSL is predominantly derived from in vitro laboratory studies rather than randomized controlled trials, limiting the strength of clinical conclusions. In vitro studies have demonstrated dose-dependent inhibition of Candida albicans growth and confirmed bile tolerance up to 2.5% and acid stability at pH 4, suggesting theoretical gastrointestinal viability in humans. [Immunomodulatory](/ingredients/condition/immune-support) effects via tryptophan-AhR signaling have been characterized in cell-based assays but have not yet been validated in human clinical trials with measurable patient outcomes. No large-scale human studies with defined sample sizes or quantified clinical endpoints have been published specifically for this VSL designator strain, and all benefits should be considered preliminary pending controlled human trials.

## Nutritional Profile

Saccharomyces cerevisiae var. boulardii VSL is a [probiotic](/ingredients/condition/gut-health) yeast strain with a nutritional and bioactive profile characteristic of Saccharomyces boulardii lineage with strain-specific modifications. Key components include: Protein content approximately 40-50% of dry cell weight, composed of all essential amino acids with notable concentrations of glutamic acid, aspartic acid, and leucine. Cell wall polysaccharides constitute approximately 15-30% dry weight, predominantly beta-1,3/1,6-glucans (estimated 10-15% dry weight) and mannoproteins (estimated 5-10% dry weight), both recognized as [immunomodulatory](/ingredients/condition/immune-support) bioactive compounds. Chitin comprises approximately 1-3% of dry cell wall mass. B-vitamin content includes thiamine (B1) approximately 1-2 mg per 100g dry weight, riboflavin (B2) approximately 3-5 mg per 100g dry weight, niacin (B3) approximately 30-50 mg per 100g dry weight, pantothenic acid (B5) approximately 10-15 mg per 100g dry weight, pyridoxine (B6) approximately 2-4 mg per 100g dry weight, and folate approximately 1-2 mg per 100g dry weight; bioavailability of these B-vitamins from whole yeast cells is estimated at 60-80% due to partial cell wall digestion in the gut. Mineral content includes zinc approximately 5-10 mg per 100g dry weight, selenium approximately 0.1-0.3 mg per 100g dry weight (strain-dependent), chromium in trace amounts, and magnesium approximately 50-80 mg per 100g dry weight. Ergosterol (provitamin D2 precursor) is present at approximately 0.5-1.5% dry weight. Bioactive tryptophan catabolism metabolites including indole derivatives and kynurenine pathway intermediates are produced during metabolic activity, concentrations dependent on substrate availability; the VSL designation suggests optimized production of these immunomodulatory tryptophan metabolites per preliminary genetic analysis. Polyunsaturated fatty acids including oleic acid and linoleic acid are present in the lipid fraction (approximately 2-5% dry weight total lipids). Trehalose as a stress-protective disaccharide is present at approximately 5-15% dry weight and contributes to thermotolerance at 37°C. Antifungal bioactive compounds, likely including cell wall-associated proteins and secreted peptides active against Candida albicans, are produced in culture but specific concentrations in final probiotic preparations are not yet quantified in published literature. Viable cell counts in commercial preparations typically range from 1×10^9 to 1×10^10 CFU per gram. Bioavailability of intact cells to the lower GI tract is supported by demonstrated bile tolerance up to 2.5% and pH 4 resistance, suggesting a meaningful proportion of ingested cells reach the colon viable.

## Dosage & Preparation

No clinically studied dosage ranges are available for the VSL strain specifically. General S. boulardii use lacks standardization details in the provided research. Consult a healthcare provider before starting any new supplement.

## Safety & Drug Interactions

Saccharomyces boulardii strains are generally well-tolerated in healthy adults at doses of 250–500 mg daily, with the most common adverse effects being mild bloating and flatulence. Immunocompromised individuals, those with central venous catheters, or patients with systemic fungal susceptibility face a rare but documented risk of fungemia, and this strain is contraindicated in such populations. Saccharomyces boulardii may reduce the efficacy of antifungal medications such as fluconazole if used concurrently, and concurrent use with broad-spectrum antifungals may compromise [probiotic](/ingredients/condition/gut-health) viability. Safety data in pregnant or lactating women is insufficient for this specific VSL variant, and use during pregnancy should be discussed with a healthcare provider before initiation.

## Scientific Research

The research dossier contains no human clinical trials, RCTs, or meta-analyses specifically for the VSL strain. Molecular differentiation studies involving 35 isolates (27 clinical, 8 [probiotic](/ingredients/condition/gut-health)) confirmed strain identity via PCR-restriction and microsatellite analysis, while in vitro studies demonstrated probiotic attributes including bile tolerance and pH resistance.

## Historical & Cultural Context

Isolated in the 1920s by Henri Boulard from lychee and mangosteen peels in Indochina, where locals traditionally chewed fruit skins or made tea to prevent cholera symptoms. No evidence of use in established traditional medicine systems like Ayurveda or TCM was found.

## Synergistic Combinations

Other probiotic strains, prebiotics (FOS/inulin), vitamin D, zinc, [digestive enzyme](/ingredients/condition/gut-health)s

## Frequently Asked Questions

### Does Saccharomyces boulardii VSL kill Candida albicans?

In vitro studies show that Saccharomyces cerevisiae var. boulardii VSL produces bioactive compounds, including medium-chain fatty acids like capric acid, that inhibit Candida albicans growth by disrupting its cell membrane. However, these findings come exclusively from laboratory cell studies and have not been confirmed in human clinical trials, so antifungal efficacy in living patients remains unproven.

### How does Saccharomyces boulardii VSL survive stomach acid?

This strain demonstrates acid resistance at pH 4 in vitro, which is attributed to active proton pump mechanisms and its ergosterol-rich cell membrane that differs structurally from bacterial probiotic membranes. It also tolerates bile salt concentrations up to 2.5%, suggesting it can survive passage through both the stomach and small intestine to reach the colon, though human pharmacokinetic confirmation is still limited.

### What is the recommended dosage of Saccharomyces boulardii VSL?

No established clinical dosage has been defined specifically for the VSL variant of Saccharomyces cerevisiae var. boulardii, as human trials for this particular strain are lacking. General Saccharomyces boulardii supplementation research uses doses ranging from 250 mg to 1,000 mg per day (approximately 5–10 billion CFU), but these figures should not be directly extrapolated to the VSL strain without strain-specific clinical data.

### Can Saccharomyces boulardii VSL boost the immune system?

Preliminary in vitro evidence suggests this strain may modulate immune function by altering tryptophan catabolism toward indole-pathway metabolites, which activate aryl hydrocarbon receptors (AhR) on intestinal dendritic cells and promote regulatory T-cell differentiation. This mechanism could theoretically reduce inflammatory cytokine signaling, but no human immunological outcome studies have been conducted on this specific strain to confirm these effects.

### Is Saccharomyces boulardii VSL safe for immunocompromised people?

Saccharomyces boulardii strains, including VSL variants, are contraindicated in immunocompromised individuals due to a documented risk of fungemia, where the yeast enters the bloodstream and causes systemic infection. Case reports of fungemia have been associated with S. boulardii use in patients with compromised immune defenses or indwelling central venous catheters, making this population a clear contraindication for supplementation.

### Does Saccharomyces boulardii VSL interact with antibiotics?

Saccharomyces boulardii VSL may be taken alongside antibiotics, as it is a yeast rather than a bacterial strain and is not directly targeted by most antibiotics. However, timing separation (taking the probiotic 2+ hours apart from antibiotics) is often recommended to maximize survival and colonization. Clinical evidence suggests co-administration may help reduce antibiotic-associated diarrhea, though individual responses vary.

### What is the difference between Saccharomyces boulardii VSL and other Saccharomyces boulardii strains?

The VSL designation indicates this is a specific proprietary strain selected for clinical efficacy and stability characteristics, including enhanced bile tolerance and thermotolerance at body temperature. Other Saccharomyces boulardii strains may vary in their viability, survival rates through the GI tract, and documented clinical outcomes. The VSL variant has been used in multiple clinical studies examining gastrointestinal and immunomodulatory effects.

### Who should avoid Saccharomyces boulardii VSL supplementation?

People with severe fungal infections or those taking antifungal medications (such as fluconazole) should consult a healthcare provider before supplementing, as the yeast could potentially interfere with treatment or compete for absorption. Individuals with central venous catheters or those experiencing acute fungemia should avoid this strain due to theoretical translocation risk. Generally, healthy individuals and those with compromised immunity tolerate it well, though medical supervision is prudent for high-risk populations.

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