A recent study conducted by the Institute of Agrochemistry and Food Technology (IATA), part of the Spanish National Research Council (CSIC), has investigated the microbial composition and immune signaling effects of eleven commercial kefirs compared to four pharmaceutical probiotics. Published in the journal Food Research International, the findings indicate “significant differences” in the ability of kefir to modulate the intestinal immune system in vitro.
The research demonstrated that this fermented milk beverage exhibits a “more complex and diverse” immunomodulatory effect, likely due to the interactions between the bacteria and yeasts present in the drink, according to a statement from the institution.
Kefir is a traditional beverage made by fermenting milk with a combination of bacteria and yeasts. Unlike yogurt, which is fermented solely by bacteria, kefir hosts a much more diverse microbial community. The IATA-CSIC study confirmed a high variability in the microbial composition, both bacterial and fungal, among the analyzed kefirs. Bacteria such as Lactococcus lactis and Streptococcus thermophilus, known for their health benefits, were predominant in many samples. Others showed a higher presence of yeasts like Kluyveromyces marxianus and Saccharomyces cerevisiae, which are associated with the production of antioxidant and immunomodulatory compounds.
Regarding the findings, Marta Arroyo, a researcher at IATA-CSIC and the study”s lead author, explained that “commercial kefirs show significant differences in their composition and effects on intestinal immune signaling pathways,” emphasizing that having clear data on their composition would assist consumers in making more informed choices.
The immune signaling pathways function as a molecular language connecting microorganisms, bioactive food compounds, intestinal cells, and the immune system. Through complex biochemical reaction cascades, these pathways enable the recognition of external signals, information transmission, and coordination of responses ranging from pathogen defense to the promotion of tolerance and immune balance.
To assess the survival capacity of the kefir microorganisms and their impact on the immune system, IATA-CSIC researchers simulated a gastrointestinal digestion process and analyzed the samples” effects on cellular models. Additionally, some kefirs exhibited notable resistance to the simulated digestive conditions, potentially allowing a greater number of viable microorganisms to reach the intestine.
The study also noted that the microbial diversity of kefir directly influences its ability to modulate various intestinal signaling pathways related to the immune system. A higher bacterial diversity correlated with a more intense activation of the aryl hydrocarbon receptor (AhR) and Toll-like receptors (TLR), which are critical proteins in regulating immune responses, while greater yeast diversity was associated with milder responses.
“This factor could enhance the immunomodulatory effects of kefir and distinguish it from some conventional probiotic supplements due to its viability for reaching the intestine and its ability to activate different signaling pathways. Moreover, interactions between the food matrix and microorganisms represent a poorly studied area that requires more attention. The balance between bacteria and fungi appears to be crucial in kefir”s ability to modulate intestinal signaling pathways,” explained Silvia Moriano, a postdoctoral researcher at IATA-CSIC and the study”s first author.
The research team emphasizes the need for precise characterization of the microorganisms present in fermented products or those containing live microorganisms, as significant differences exist among the analyzed kefirs despite sharing the same product definition. “Given the observed differences between brands and formulations, it would be advisable for manufacturers to include more detailed information about microbial composition and viability on labels, not only for kefirs but also for other fermented products,” Arroyo noted.
The research team is currently working to identify the microbial strains and metabolites responsible for these effects, and they stress the importance of conducting clinical trials in humans to confirm their physiological relevance, considering the complexity of establishing causal relationships and responses associated with individual diets.
