Does "Daily Kimchi" Work During Cold Season? — New Research Focuses on "Balancing" Immunity Rather Than "Boosting" It

Rather than "boosting immunity," it's harder to "prevent it from overreacting"

In winter, respiratory illnesses like colds and flu become a hot topic, and "foods that boost immunity" trend every year. In December 2025, ScienceDaily highlighted a study claiming that kimchi not only boosts immunity but also helps regulate it by preventing overreactions, drawing significant attention. ScienceDaily

However, the key point this time is not just "boosting immunity." A strong immune system is not always beneficial; if it overacts, it can lead to inflammation or autoimmune issues. Ideally, the immune system should respond quickly and strongly only when needed and remain calm otherwise—in other words, maintaining "immune balance (homeostasis)." Researchers aimed to explore kimchi's potential role in this balance using cutting-edge "single-cell analysis." Nature

Study details: Does eating kimchi change the "conversation" of immune cells?

The original paper was published in npj Science of Food, evaluating immune cells in the blood (PBMC) using single-cell RNA sequencing (scRNA-seq). This method reads which types of immune cells in the same blood are activating which genes and to what extent, at the single-cell level. Unlike traditional "bulk analysis," this approach makes it easier to see subtle changes and movements of minority cell populations that might be hidden in average values. Nature

According to the paper's abstract, after 12 weeks of intervention, there was a strengthening of intercellular signals mediated by cells involved in antigen presentation (e.g., dendritic cells), with suggested increases in antigen uptake and expression of MHC class II-related genes (JAK/STAT1–CIITA pathway). Additionally, CD4-positive T cells showed a balanced differentiation towards both "effector" roles in defense and "regulatory" roles in suppression, while CD8-positive T cells, B cells, and NK cells remained largely stable, suggesting the potential maintenance of systemic immune homeostasis. Nature

Caution: The number of participants differs between the article and the paper

A common point of contention on social media is, "So, how many participants were in the trial?" The ScienceDaily introduction mentions "dividing overweight adults into three groups (n=13 each)." ScienceDaily

On the other hand, the abstract and results section of the original paper indicate that the single-cell analysis involved **13 individuals (4 placebo, 5 naturally fermented kimchi, 4 starter fermented kimchi)**, extracted for detailed analysis from an original randomized double-blind placebo-controlled trial involving 90 participants. Nature

Rather than "which is correct," it might be safer for readers to understand it as "there is a separate clinical trial population, with a portion subjected to ultra-detailed analysis." Single-cell analysis is costly and labor-intensive. Therefore, while it allows for deep exploration even with few subjects, the small number also means caution is necessary. Nature

Does the fermentation method make a difference?—Why "starter fermentation" is gaining attention

Another point of discussion is the fermentation method of kimchi. Comparisons between natural fermentation (spontaneous) and fermentation using starter cultures suggest that while both may contribute to immune balance, starter fermentation shows a stronger effect. ScienceDaily

As food research leans more towards "functionality," reproducibility and quality control become crucial. Starter fermentation not only stabilizes flavor and quality but might also target health functions. Conversely, the future might see a world where "not all kimchi is the same," with differences based on strains and processes. Nature

So, the conclusion: Does eating kimchi prevent colds?

It's tempting to declare, "Eat kimchi every day and be invincible!" However, the paper mainly demonstrates changes in gene expression and intercellular signaling of immune cells, and does not directly prove actual infection prevention (e.g., reduced number of colds). Furthermore, the intervention was in powder or capsule form, which doesn't entirely match kimchi as part of a regular diet. Nature

Nonetheless, the value lies in not leaving the "effects of fermented foods" as a vague sensation but attempting to concretize which parts of the immune system move and how at the cellular level. In today's climate of overheated health information, it's crucial to move beyond a binary "works/doesn't work" perspective to a nuanced understanding of "which cells, in which direction, and to what extent." Nature

SNS reactions: Enthusiasm and skeptical comments ran simultaneously

1) Experts spreading the word: Introduced as "#clinicaltrial"

On social media, posts emphasizing the clinical trial aspect were shared. For instance, a post by someone with credentials in the vaccine and infectious disease field summarized the abstract as "In a 12-week clinical trial, kimchi acts as a 'precision regulator' of immunity," spreading it with a link, as cited in an overseas article (posted on November 26, 2025). SinEmbargo MX

2) Skepticism: Pointing out the "usual" in food research

Conversely, on Reddit's food community, discussions were quite candid. In related threads, considering the research was conducted by a kimchi research institution, a top comment questioned, "Isn't it typical for a food organization to release research saying 'this food is good'?" Reddit

Such reactions reflect a recurring "wariness" in the context of health research.

3) Yet, some praise: Citing "peer-reviewed," "double-blind," "placebo-controlled" to defend

In the same thread, another user highlighted aspects like "npj Science of Food is peer-reviewed, and the trial was randomized, double-blind, and placebo-controlled," to commend the research's credibility. Reddit

Additionally, the paper mentions "no competing interests" regarding conflicts of interest. PubMed

4) In the Japanese sphere, the phrase "precision regulator" resonated

In the Japanese sphere, articles introducing the study as an "immune system 'precision regulator'" have appeared, functioning as a catchy phrase likely to trend. note（ノート）

Summary: The "next highlights" of kimchi research

What makes this research intriguing is its attempt to "deconstruct" the qualitative image of "kimchi = seems healthy" with single-cell level data. While changes in antigen presentation systems and CD4-positive T cells are suggested, the number of analyzed participants is limited, and it doesn't directly translate to clinical outcomes (like infection rates). Nature

Future focuses are likely threefold.
(1) Whether similar immune changes are replicated in larger populations.
(2) Whether it connects to actual health and infection indicators.
(3) Whether it becomes clear which kimchi, based on fermentation methods, strains, and manufacturing processes, is associated with which effects. Nature

The divide on SNS between "kimchi is the best!" and "it's overhyped!" is the fate of health topics. But this is precisely why it's valuable to return to the content of the paper and read it from the perspective of "regulating immunity" rather than "boosting immunity." Nature