News | Can Drinking Kefir Really Improve Gut Health? New Research Offers a More Cautious Answer
In recent years, kefir, a traditional fermented dairy product, has gained worldwide popularity for being “rich in probiotics,” with many consumers viewing it as a natural way to improve gut health and strengthen immunity. A systematic review recently published in the international journal Nutrients, however, concludes that although kefir may alter some microbial communities in the gut and mouth, consistent, robust scientific evidence for its actual health effects is still lacking.
The review, conducted by a team of scientists, systematically assessed published human studies, focusing on how kefir consumption affects the gut and oral microbiomes. The findings indicate that kefir may cause changes in specific microbial niches, but the clinical significance remains unclear because studies are generally small and their designs vary widely.
From a Traditional Caucasus Drink to a Subject of Modern Research
Kefir originated in the Caucasus Mountains and has been consumed for more than 3,000 years. It is fermented using “kefir grains,” a complex symbiotic community of lactic acid bacteria, acetic acid bacteria and yeasts enclosed in a polysaccharide matrix. When added to milk, the grains trigger natural fermentation, gradually thickening the milk and producing a mildly tart flavor.
In addition to cow's milk, kefir can be made from goat's milk, sheep's milk or even soy milk. Industrial production generally adds grains to milk at a ratio of 1:30 to 1:50 and ferments the mixture at room temperature for up to 24 hours. The grains are then filtered out, and the drink is consumed or refrigerated.
Researchers noted that the highly variable composition of kefir is a major challenge in evaluating its health effects. The fermentation base, origin of the grains, fermentation time and temperature can all substantially affect the types and proportions of microorganisms in the final drink and the bioactive metabolites they produce. Kefir products used in different studies therefore often are not comparable.
Microorganisms in Kefir: Potential and Variability
The predominant microorganisms in kefir are lactic acid bacteria (LAB), including Lentilactobacillus kefiri, Leuconostoc mesenteroides and Lactococcus lactis. These species break down lactose to produce lactic acid and also generate substances such as bacteriocins and hydrogen peroxide that inhibit some intestinal pathogens.
L. kefiri and L. mesenteroides can survive passage through the gastrointestinal tract and adhere to the intestinal epithelium, characteristics typical of probiotics. Studies have also found that L. kefiri can bind heavy metals and mycotoxins, suggesting possible toxicological applications, while L. mesenteroides produces linoleic acid, which may have anti-inflammatory, anti-atherosclerotic and anticancer effects.
Kefir also contains various acetic acid bacteria, including Acetobacter and Gluconobacter species. The acetic acid and related metabolites they produce are thought to support intestinal motility, improve blood flow in the colon and maintain intestinal epithelial homeostasis.
Yeasts are another important component, including Saccharomyces cerevisiae and several Kluyveromyces species. They produce small amounts of ethanol and carbon dioxide, giving kefir its distinctive flavor and mild effervescence. The boulardii variety of S. cerevisiae has shown antimicrobial, anti-inflammatory and antioxidant potential in multiple studies and may help manage irritable bowel syndrome and Crohn's disease.
Effects on Gut and Oral Microbes: Inconsistent Findings
Responses to kefir vary considerably across populations. Some healthy adults showed only a small, statistically nonsignificant increase in Lactococcus lactis after drinking it, while people with metabolic syndrome and inflammatory bowel disease (IBD) showed increases in Actinobacteria and Lactobacillus abundance, respectively.
Among critically ill patients, kefir consumption improved the “gut microbiome health index” despite a reduction in microbial diversity. Women with polycystic ovary syndrome (PCOS) had a significant increase in Bacillus abundance after drinking kefir, along with marked improvements in physical fitness and mental health scores compared with before the intervention.
Notably, even when increases in lactic acid bacteria were modest, some studies in people with metabolic syndrome found within-group improvements in fasting insulin, inflammatory markers such as TNF-α and IFN-γ, and blood pressure. This suggests microbial changes may be related to systemic health effects.
Evidence on the oral microbiome is even more limited. Only 4 studies have evaluated kefir's effects on oral bacteria, and their findings suggest it may reduce salivary levels of Streptococcus mutans, an important cause of tooth decay in adults and children.
Researchers emphasized, however, that all these studies relied on traditional culture methods, which cannot fully capture the overall oral microbiome and did not use DNA sequencing. Kefir's true effect on oral microbial diversity therefore remains unknown.
Conclusion: Potential Benefits, but Insufficient Evidence
Overall, current research suggests that kefir may affect gut and oral microorganisms, but substantial uncertainty remains about the strength, consistency and clinical significance of these effects. Differences among kefir products, inconsistent study designs and small sample sizes all limit firm conclusions about long-term health effects.
The researchers called for larger, more rigorous and longer clinical studies using standardized kefir products and modern sequencing technologies to clarify the role of this traditional fermented drink in human health.
News | Can Drinking Kefir Really Improve Gut Health? New Research Offers a More Cautious Answer
News | Can Drinking Kefir Really Improve Gut Health? New Research Offers a More Cautious Answer
In recent years, kefir, a traditional fermented dairy product, has gained worldwide popularity for being “rich in probiotics,” with many consumers viewing it as a natural way to improve gut health and strengthen immunity. A systematic review recently published in the international journal Nutrients, however, concludes that although kefir may alter some microbial communities in the gut and mouth, consistent, robust scientific evidence for its actual health effects is still lacking.
The review, conducted by a team of scientists, systematically assessed published human studies, focusing on how kefir consumption affects the gut and oral microbiomes. The findings indicate that kefir may cause changes in specific microbial niches, but the clinical significance remains unclear because studies are generally small and their designs vary widely.
From a Traditional Caucasus Drink to a Subject of Modern Research
Kefir originated in the Caucasus Mountains and has been consumed for more than 3,000 years. It is fermented using “kefir grains,” a complex symbiotic community of lactic acid bacteria, acetic acid bacteria and yeasts enclosed in a polysaccharide matrix. When added to milk, the grains trigger natural fermentation, gradually thickening the milk and producing a mildly tart flavor.
In addition to cow's milk, kefir can be made from goat's milk, sheep's milk or even soy milk. Industrial production generally adds grains to milk at a ratio of 1:30 to 1:50 and ferments the mixture at room temperature for up to 24 hours. The grains are then filtered out, and the drink is consumed or refrigerated.
Researchers noted that the highly variable composition of kefir is a major challenge in evaluating its health effects. The fermentation base, origin of the grains, fermentation time and temperature can all substantially affect the types and proportions of microorganisms in the final drink and the bioactive metabolites they produce. Kefir products used in different studies therefore often are not comparable.
Microorganisms in Kefir: Potential and Variability
The predominant microorganisms in kefir are lactic acid bacteria (LAB), including Lentilactobacillus kefiri, Leuconostoc mesenteroides and Lactococcus lactis. These species break down lactose to produce lactic acid and also generate substances such as bacteriocins and hydrogen peroxide that inhibit some intestinal pathogens.
L. kefiri and L. mesenteroides can survive passage through the gastrointestinal tract and adhere to the intestinal epithelium, characteristics typical of probiotics. Studies have also found that L. kefiri can bind heavy metals and mycotoxins, suggesting possible toxicological applications, while L. mesenteroides produces linoleic acid, which may have anti-inflammatory, anti-atherosclerotic and anticancer effects.
Kefir also contains various acetic acid bacteria, including Acetobacter and Gluconobacter species. The acetic acid and related metabolites they produce are thought to support intestinal motility, improve blood flow in the colon and maintain intestinal epithelial homeostasis.
Yeasts are another important component, including Saccharomyces cerevisiae and several Kluyveromyces species. They produce small amounts of ethanol and carbon dioxide, giving kefir its distinctive flavor and mild effervescence. The boulardii variety of S. cerevisiae has shown antimicrobial, anti-inflammatory and antioxidant potential in multiple studies and may help manage irritable bowel syndrome and Crohn's disease.
Effects on Gut and Oral Microbes: Inconsistent Findings
Responses to kefir vary considerably across populations. Some healthy adults showed only a small, statistically nonsignificant increase in Lactococcus lactis after drinking it, while people with metabolic syndrome and inflammatory bowel disease (IBD) showed increases in Actinobacteria and Lactobacillus abundance, respectively.
Among critically ill patients, kefir consumption improved the “gut microbiome health index” despite a reduction in microbial diversity. Women with polycystic ovary syndrome (PCOS) had a significant increase in Bacillus abundance after drinking kefir, along with marked improvements in physical fitness and mental health scores compared with before the intervention.
Notably, even when increases in lactic acid bacteria were modest, some studies in people with metabolic syndrome found within-group improvements in fasting insulin, inflammatory markers such as TNF-α and IFN-γ, and blood pressure. This suggests microbial changes may be related to systemic health effects.
Evidence on the oral microbiome is even more limited. Only 4 studies have evaluated kefir's effects on oral bacteria, and their findings suggest it may reduce salivary levels of Streptococcus mutans, an important cause of tooth decay in adults and children.
Researchers emphasized, however, that all these studies relied on traditional culture methods, which cannot fully capture the overall oral microbiome and did not use DNA sequencing. Kefir's true effect on oral microbial diversity therefore remains unknown.
Conclusion: Potential Benefits, but Insufficient Evidence
Overall, current research suggests that kefir may affect gut and oral microorganisms, but substantial uncertainty remains about the strength, consistency and clinical significance of these effects. Differences among kefir products, inconsistent study designs and small sample sizes all limit firm conclusions about long-term health effects.
The researchers called for larger, more rigorous and longer clinical studies using standardized kefir products and modern sequencing technologies to clarify the role of this traditional fermented drink in human health.
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