Saccharomyces cerevisiae is a yeast species widely recognized for its roles in baking and brewing, but specific strains are cultivated for use as probiotics. A probiotic is a live microorganism that, when consumed in adequate amounts, confers a health benefit. Unlike the majority of probiotics which are bacteria, S. cerevisiae offers a unique, non-bacterial option for supporting gut health. The most researched of these is Saccharomyces cerevisiae var. boulardii. This strain was first isolated in 1923 by French scientist Henri Boulard, who observed people in Southeast Asia chewing on the skins of lychee and mangosteen to counter symptoms of cholera.
Distinguishing Probiotic Yeast from Common Yeast
While yeasts for baking, brewing, and probiotics belong to the same species, they are genetically distinct strains with different properties. Strains used in baking and brewing are selected for metabolic capabilities, like producing carbon dioxide for bread or alcohol for beer, and are not cultivated to withstand the digestive system.
Probiotic yeast, specifically the Saccharomyces boulardii strain, is selected for its therapeutic characteristics. A defining feature is its ability to grow at human body temperature, approximately 37°C (98.6°F), and to tolerate stomach acid and bile salts. This resilience allows it to reach the intestines alive, where it can exert its beneficial effects, while most baker’s and brewer’s yeasts are inactivated by these conditions.
How It Functions in the Digestive System
Once it arrives in the intestines, probiotic S. cerevisiae does not permanently colonize the gut but acts as a transient, beneficial resident. This temporary presence is enough to initiate several positive changes within the intestinal environment.
One of its primary functions is competitive exclusion, where the yeast competes with harmful bacteria for physical space on the intestinal lining and for nutrients. This competition makes it more difficult for pathogens to establish themselves and multiply. Probiotic yeast can also adhere to certain pathogenic bacteria, preventing them from binding to the intestinal wall and helping to clear them from the gut.
Beyond competition, S. cerevisiae actively neutralizes bacterial toxins. It produces proteins that can break down and inactivate the toxins produced by harmful bacteria like Clostridium difficile and E. coli, mitigating the damage they can cause.
This probiotic yeast also modulates the host’s immune system. By interacting with immune cells in the gut wall, it helps promote a balanced immune response, reducing the secretion of pro-inflammatory molecules. It also supports the integrity of the gut barrier, helping to strengthen the junctions between intestinal cells.
Therapeutic Uses and Health Benefits
One of the most extensively studied applications of probiotic S. cerevisiae is for digestive health, where it has been shown to provide several benefits.
- Manages and prevents diarrhea: It has proven effective against several types, including antibiotic-associated diarrhea (AAD). It is also beneficial for managing traveler’s diarrhea and infectious diarrhea caused by various pathogens.
- Alleviates Irritable Bowel Syndrome (IBS) symptoms: Research indicates this probiotic can help relieve common issues such as abdominal pain, bloating, and irregular bowel movements by helping to restore a more balanced intestinal environment.
- Supports Inflammatory Bowel Disease (IBD) therapy: While not a standalone treatment, it can act as an adjunct therapy for conditions like Crohn’s disease and ulcerative colitis, helping to maintain remission and reduce the inflammatory response in the gut.
- Combats pathogenic infections: It can support the body against specific pathogens. It has been used to aid in the elimination of Helicobacter pylori, the bacterium associated with stomach ulcers, when used with standard medical treatments, and it also shows inhibitory effects against the overgrowth of Candida albicans.
Considerations for Use and Supplementation
Saccharomyces cerevisiae probiotics are available as dietary supplements, sold in capsule or powder form. These products can be found in health food stores, pharmacies, and online. When choosing a supplement, it is important to check the label for the specific strain, which is most often Saccharomyces boulardii, and the number of colony-forming units (CFUs) to ensure a therapeutic dose.
The supplement is generally well-tolerated by most people. When side effects do occur, they are usually mild and temporary, most commonly consisting of gas or bloating as the digestive system adjusts. These symptoms often subside after a few days of consistent use. Starting with a lower dose and gradually increasing it can help minimize potential discomfort.
Despite its strong safety profile, there are important contraindications. Individuals who are severely immunocompromised or those with a central venous catheter (a type of IV line) should avoid using this probiotic. In these specific populations, there is a small risk of fungemia, a condition where the yeast enters the bloodstream and causes a systemic infection. Therefore, it is always recommended to consult with a healthcare provider before beginning supplementation, especially for those with underlying health conditions or who are taking other medications.