A study conducted by the Instituto de Agroquímica y Tecnología de Alimentos (IATA), part of the Consejo Superior de Investigaciones Científicas (CSIC), has examined the microbial composition and signaling effects of eleven commercial kefirs compared to four pharmaceutical probiotics. Published in the journal Food Research International, the research indicates “significant differences” in the ability of kefir to modulate the intestinal immune system in vitro.
The findings suggest that this fermented milk beverage has a “more complex and diverse” immunomodulatory effect, likely due to the interaction between the bacteria and yeasts present in the drink, according to a statement from the institution. Kefir is a traditional beverage created through the fermentation of milk, using a combination of bacteria and yeasts. Unlike yogurt, which is fermented solely by bacteria, kefir hosts a much more diverse microbial community.
The study confirmed high variability in the microbial composition, both bacterial and fungal, of the analyzed kefirs. Predominant bacteria included Lactococcus lactis and Streptococcus thermophilus, which are common in dairy fermentation and beneficial for gut health. Additionally, some samples showed a higher presence of yeasts like Kluyveromyces marxianus and Saccharomyces cerevisiae, which are associated with the production of compounds that exhibit antioxidant and immunomodulatory effects.
Marta Arroyo, a researcher at IATA-CSIC and the lead author of the study, noted that “commercial kefirs show significant differences in their composition and effects on intestinal immune signaling pathways,” emphasizing the need for clear data on their composition to enable consumers to make informed choices.
The immune signaling pathways function as a molecular language connecting microorganisms, bioactive food compounds, intestinal cells, and the immune system. These pathways facilitate the recognition of external signals, the transmission of information, and the coordination of responses ranging from pathogen defense to the promotion of tolerance and immune balance.
To assess the survival capacity of kefir microorganisms and their impact on the immune system, researchers from IATA-CSIC simulated gastrointestinal digestion and analyzed the effects of the samples in cellular models. Remarkably, some kefirs demonstrated notable resistance to simulated digestive conditions, which could enhance the arrival of a greater number of live microorganisms to the intestine.
The study also found that the microbial diversity of kefir directly influences its ability to modulate various intestinal signaling pathways related to the immune system. Greater bacterial diversity was associated with a more intense activation of the aryl hydrocarbon receptor (AhR) and Toll-like receptors (TLR), which are crucial proteins in regulating the immune response, while higher yeast diversity correlated with more subdued responses.
This aspect could enhance the immunomodulatory effects of kefir and distinguish it from some conventional probiotic supplements due to its viability in reaching the intestine and activating different signaling pathways. Furthermore, the interactions between the food matrix and microorganisms represent a poorly explored area that requires further attention. The balance between bacteria and fungi appears to be decisive in kefir”s capacity to modulate intestinal signaling pathways, explained Silvia Moriano, a postdoctoral researcher at IATA-CSIC and the study”s first author.
The research highlights the importance of accurately characterizing the microorganisms present in fermented products or those containing live microorganisms. Despite being classified under the same product definition, significant differences exist among the analyzed kefirs. “Given the differences observed between brands and formulations, it would be advisable for manufacturers to provide more detailed information regarding microbial composition and viability on labels, not only for kefirs but also for other fermented products,” Arroyo stated.
The research team is currently working to identify the microbial strains and metabolites responsible for these effects, emphasizing the necessity of conducting clinical trials in humans to confirm their physiological relevance, considering the complexity of establishing causal relationships and diet-related responses in individuals.
