Friendly Fungi: How Yeasts Support Your Microbiome and Immune System

By Julia Haimovich, Accredited Practicing Dietitian.

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FerFit Dietetics &  Nutrition

Yeasts are naturally present in the human body, though many people mainly think of them in connection with infections. Current research paints a more nuanced picture: yeasts are not inherently harmful. Some play essential roles in health, while others only become problematic under certain conditions. Beneficial yeasts contribute to digestion, support the immune system, and help maintain microbial equilibrium, whereas opportunistic species can cause issues when the body’s internal environment is disrupted. The 2023 review by Caetano et al. offers one of the latest comprehensive insights on this topic (1). Maintaining a stable microbiome through a balanced diet, stress management, and, when appropriate, evidence-based yeast probiotics can help sustain harmony between beneficial and opportunistic species (1-5).

Q1: What are yeasts exactly?

Yeasts are unicellular fungi that inhabit the skin, gastrointestinal tract, and surrounding environment. Many, such as Saccharomyces cerevisiae, are harmless or beneficial, while species like Candida albicans are opportunistic and only cause disease when the body’s microbial balance is disturbed (1,2).

Q2: Are yeasts always harmful?

Not at all. Certain yeasts provide essential functions in digestion, gut barrier integrity, and immune modulation. Saccharomyces boulardii, one of the most studied yeast probiotics, has been shown to restore gut microbial balance, particularly after antibiotic treatment (1,3).

Q3: How do yeasts contribute to gut and immune health?

Beneficial yeasts help strengthen the intestinal lining, inhibit pathogenic microbes from attaching, regulate immune activity, and reduce inflammation through bioactive compounds (1,3). Components derived from yeast, such as β-glucans, also activate immune pathways that protect the body (4).

Q4: When can yeasts become harmful?

Opportunistic yeasts overgrow when the internal environment is altered such as during immune suppression, elevated stress, antibiotic use, poorly controlled diabetes, or high-sugar diets (1,2). Under these conditions, species like Candida albicans can transition from harmless residents to pathogenic organisms (2).

Q5: Do diet and lifestyle influence yeast infections?

While diet alone doesn’t directly cause yeast infections, high sugar intake and poor blood sugar control can promote overgrowth. Vaginal pH, mucosal immunity, hormonal fluctuations, and microbiome balance are stronger determinants (2,5). Eating a balanced diet supports a stable internal environment that discourages opportunistic overgrowth.

Q6: Are yeast probiotics effective?

Yes. S. boulardii has demonstrated clinical benefits for antibiotic-associated diarrhoea, traveller’s diarrhoea, and microbiota restoration (3). Research also shows benefits for gut barrier function and certain inflammatory conditions (1,3). Yeast probiotics act transiently without permanently colonising the gut, making them generally safe for most people.

Q7: Which foods naturally provide beneficial yeasts?

Several common foods contain beneficial yeasts that promote gut health and microbial balance. Examples include kefir, sourdough bread, kombucha, and other fermented dairy products. These foods often contain Saccharomyces species, particularly S. boulardii, which can aid digestion, restore the microbiome after antibiotics, and support immune function (2,3,6). Including these in a balanced diet can help maintain gut health and microbial stability.

References

  1. Caetano CF, Gaspar C, Martinez-de-Oliveira J, Palmeira-de-Oliveira A, Rolo J. The role of yeasts in human health: a review. Life (Basel). 2023;13(4):924. doi:10.3390/life13040924. PMID:37109452; PMCID:PMC10143383.
  2. Calderone RA, Clancy CJ. Candida and Candidiasis. 2nd ed. Washington, DC: ASM Press; 2012.
  3. Kelesidis T, Pothoulakis C. Efficacy and safety of the probiotic Saccharomyces boulardii for prevention and therapy of gastrointestinal disorders. Therap Adv Gastroenterol. 2012;5(2):111–125. doi:10.1177/1756283X11428502.
  4. Brown GD, Gordon S. Immune recognition of fungal β-glucans. Cell Microbiol. 2005;7(4):471–479. doi:10.1111/j.1462-5822.2005.00505.x.
  5. Sobel JD. Vulvovaginal candidosis. Lancet. 2007;369(9577):1961–1971. doi:10.1016/S0140-6736(07)60917-9.
  6. Pereira DI, Gibson GR. Effects of consumption of probiotics and prebiotics on serum lipid levels in humans. Crit Rev Biochem Mol Biol. 2002;37(4):259–281. doi:10.1080/10409230290771501.