Interview: Can fermented foods support oral and gut health?

Iveta Ramonaite, Dental Tribune International

Tue. 1. September 2026

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Fermented foods are increasingly being studied for their potential to influence the human microbiome, but research has focused predominantly on the gut, leaving their interaction with the oral microbiome comparatively under-explored. A recent review has examined how microorganisms and bioactive components in fermented foods may interact with microbial communities across the oral–gut axis. Dental Tribune International spoke with the authors, Dr Dongyeop Kim from the School of Dentistry at Jeonbuk National University in Jeonju in South Korea and Prof. Hyun Michel Koo, co-founding director of the Center for Innovation and Precision Dentistry at the University of Pennsylvania in Philadelphia in the US. In this interview, they discuss current evidence on fermented foods, the implications for oral health and the potential for microbiome-informed prevention.

Your review considers fermented foods in relation to both the oral and gut microbiota. Why has research traditionally focused more on the gut microbiome, and why is it important to consider the oral microbiome as well?
Dr Kim: Most research on fermented foods has focused on the gut because the gut microbiome has been extensively studied in relation to nutrition and systemic health. However, the oral cavity is the first point of contact between the fermented food microbiome and the human microbiome.

During chewing, microorganisms and metabolites from fermented foods come into direct contact with dental and mucosal surfaces before entering the gastro-intestinal tract. The oral cavity is therefore not simply a passage to the gut but an important biological interface where diet can influence microbial ecology and function. Including the oral microbiome may help us understand the effects of fermented foods across the entire oral–gut axis and their impact on health.

What does the current evidence tell us about how fermented foods interact with the oral microbiota and whether they can alter it?
Dr Kim: Current evidence suggests that fermented foods can influence the oral microbiota by introducing live microorganisms and their metabolites that interact with resident microbiota. Some lactic acid bacteria can compete with potentially pathogenic microorganisms by producing antimicrobial compounds and influencing biofilm formation.

Are these effects mainly temporary, or is there evidence of more lasting changes?
Dr Kim: The evidence currently supports transient interactions rather than permanent colonisation. Regular consumption may repeatedly expose the oral microbiome to the fermented food microbiome, potentially influencing microbial community structure and function without requiring long-term colonisation. However, we still need longitudinal human studies as well as mechanistic studies to determine whether these effects persist over time.

Your review places considerable emphasis on the oral–gut axis. How might interactions between fermented foods and the oral microbiota ultimately affect the gut microbiota or systemic health?
Dr Kim: The oral and gut microbiomes are interconnected microbial ecosystems. Oral and food-derived microorganisms are regularly swallowed, and some survive passage through the gastro-intestinal tract. Therefore, changes occurring in the mouth may influence downstream microbial communities. Fermented foods may also act through microbial metabolites and immune signalling rather than simply through microbial colonisation. These interactions could influence gut barrier function, inflammatory responses and metabolic processes. However, direct evidence that changes in the oral microbiome induced by fermented foods subsequently improve systemic health remains limited. This is an important area for future research and one that our group is currently investigating.

“The oral and gut microbiomes are interconnected microbial ecosystems.”—Dr Dongyeop Kim, Jeonbuk National University

From an oral health perspective, what evidence is there that fermented foods or their microorganisms could influence the risk of caries or periodontitis?
Prof. Koo: The evidence is limited and mostly from benchtop studies showing that certain lactic acid bacteria found in fermented foods can interfere with biofilm formation by pathogenic bacteria. Laboratory-based data also suggests potential modulation of local immune and inflammatory responses, which may be relevant to periodontal health. However, these effects are highly strain- and context-dependent and require further mechanistic and in vivo investigation, as well as longitudinal clinical data.

Furthermore, not all lactic acid bacteria are necessarily beneficial to oral health, and some fermented foods, particularly those that are acidic or contain fermentable sugars, could potentially contribute to enamel demineralisation under certain conditions. Therefore, fermented foods should not simply be regarded as universally protective against oral disease.

How strong is the clinical evidence at present, and what are the main limitations?
Prof. Koo: The clinical evidence is limited and insufficient to recommend fermented foods specifically as a treatment or preventive intervention for oral diseases, including caries and periodontitis. Most of the evidence comes from laboratory studies and some animal studies, and clinical data remains scarce. In addition, there is variation in the fermented foods and microbial composition studied and the design of human studies. Given the available evidence and the potential beneficial effects of the fermented food microbiome, there is a clear motivation for further clinical investigation, including longitudinal studies and in-depth mechanistic research.

Are we at a point where dentists can reasonably discuss fermented foods as part of preventive oral health advice, or would that be premature?
Prof. Koo: Fermented foods can be considered as part of a balanced and diverse diet, but specific claims that fermented foods prevent oral disease are premature. To move forward, we still need well-controlled clinical trials that assess oral health outcomes and in-depth mechanistic studies, as outlined in our review’s precision nutrition road map.

If dental professionals were to take one message from your review about the relationship between diet, the oral microbiome and systemic health, what should it be?
Prof. Koo: One key message is that the mouth is not separate from the body. It is the first microbial checkpoint for everything we eat. Everything we eat encounters the oral environment and its microbial communities before reaching the gut, so oral health professionals have an important role in understanding how diet shapes both oral and systemic health.

Fermented foods are an especially compelling example because they deliver microorganisms, microbial metabolites and dietary substrates within a single food matrix. By understanding how this “edible microbiome” interacts with the oral and gut microbiota and may shape immune and metabolic responses, dental professionals can help move nutrition advice towards more microbiome-informed strategies for supporting oral and systemic health.

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