Yeasts and Your Health Helpful Friends or Hidden Foes?

Natural dietary sources of beneficial yeasts: kefir, sourdough bread, kombucha.

Yeasts are a natural part of human life, yet many people associate them only with infections. Current scientific evidence shows a much more balanced picture. Yeasts are not automatically harmful. Some are essential for health, while others require balance and appropriate internal conditions. Beneficial yeasts support digestion, protect the immune system, and help maintain microbial stability, while opportunistic species may cause problems only in certain conditions. The 2023 review by Caetano and colleagues provides one of the most up-to-date summaries on this topic (1). A stable microbiome, balanced diet, stress control, and occasional use of evidence-based yeast probiotics help maintain the harmony between beneficial and opportunistic species (1–5).

Q1: What exactly are yeasts?

Yeasts are single-celled fungi that live on the skin, in the gut, and in the environment. Many species, such as Saccharomyces cerevisiae, are harmless or helpful, while others like Candida albicans are opportunistic and can cause disease only when balance is disrupted (1,2).

Q2: Are yeasts always harmful?

No. Beneficial yeasts play important roles in digestion, gut integrity, and immune modulation. Saccharomyces boulardii is one of the most researched yeast probiotics, shown to improve gut function and restore microbiota balance after antibiotics (1,3).

Q3: How do yeasts support gut and immune health?

Research shows that beneficial yeasts strengthen the gut barrier, prevent pathogen adhesion, regulate immune responses, and reduce inflammation through bioactive metabolites (1,3). Yeast-derived components such as β-glucans also stimulate protective immune pathways (4).

Q4: When do yeasts become a problem?

Opportunistic species overgrow when the environment changes for example during immune suppression, high stress, antibiotic use, poorly controlled diabetes, or high-sugar diets (1,2). This allows species like Candida albicans to shift from harmless commensal to pathogenic behaviour (2).

Q5: Are vaginal or skin yeast infections caused by diet?

Diet alone doesn’t directly cause infection, but high sugar intake and poor glycaemic control make yeast overgrowth more likely. Vaginal pH, mucosal immunity, microbiota balance, hormones, and moisture are stronger determinants (2,5). Balanced nutrition helps maintain a stable internal environment.

Q6: Do yeast probiotics actually work?

Yes. S. boulardii is clinically proven to help with antibiotic-associated diarrhoea, traveller’s diarrhoea, and microbiota restoration (3). Evidence also shows benefits in inflammatory conditions and improved gut barrier function (1,3). Yeast probiotics act temporarily and do not permanently colonise the gut, making them safe for many individuals.

Q7: Which foods naturally contain beneficial yeasts?

Several everyday foods contain beneficial yeasts that support gut health and microbiome balance. Key examples include kefir, sourdough bread, kombucha, and fermented dairy products. These foods often contain Saccharomyces species, particularly Saccharomyces boulardii, which has been shown to improve digestion, restore microbiota after antibiotics, and support immune function (2,3,6). Including these foods in a balanced diet may help maintain microbial stability and overall gut health.

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. (Peer-reviewed academic monograph widely cited in clinical mycology.)

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