Kefir: a natural ally for our gut microbiota?

Kefir is a fermented beverage native to the Caucasus, Eastern Europe, and the Balkans, where people have been drinking it for centuries. Today, kefir is making a worldwide comeback. Made with either water or milk, it is prepared using kefir “grains”: small white or translucent clusters containing a mixture of lactic acid bacteria, acetic acid bacteria, and yeast within a matrix of polysaccharides and proteins.
This microscopic ecosystem transforms milk or sugar water into a tangy, slightly sparkling beverage rich in fermentation-derived compounds that contribute to the drink’s nutritional value.

There are two main types:

• milk kefir, which has been studied most extensively,
• and water kefir, typically prepared with sugar water, and sometimes with nuts, dried fruit or lemon.

The composition of kefir varies greatly depending on the grains used, the type of milk or sugar, the temperature, the fermentation time, and storage conditions. This microbial diversity is precisely what makes kefir so beneficial: it may influence our gut microbiota and, through it, a range of key bodily functions—from digestion to immunity—much like other fermented foods such as kombucha ^1,2,3,4.

Does kefir really “feed” our gut microbiota?

Kefir is often described as a “functional food”—one that may provide health benefits beyond its basic nutritional value. Human studies suggest that kefir may have promising effects on the gut microbiota, digestion, certain markers of inflammation, metabolism, and immunity. Its primary site of action appears to be the gut microbiota. By delivering live microorganisms with a probiotic effect, along with compounds produced during fermentation, kefir may help promote a more diverse and active gut microbiota. In particular, some studies have shown an increase in bacteria involved in the production of short-chain fatty acids (sidenote: Short chain fatty acids (SCFA) Short chain fatty acids (SCFA) are a source of energy (fuel) for an individual’s cells. They interact with the immune system and are involved in communication between the intestine and the brain. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25. ) —molecules that are essential for the intestinal barrier and for communication between the gut microbiota, the immune system, and metabolism ^1,2,5. 

That said, caution is still advised: not all kefirs are the same, and studies use very different doses, durations, and recipes. Therefore, kefir shows considerable promise, but we should not yet attribute universal health powers to it, nor should we assume that all products offer the same benefits.

Could kefir benefit our oral microbiota? 

Our mouth also has its own microbiota. When this microbiota is out of balance, certain bacteria can contribute to cavities, enamel erosion, and gum disease. Preliminary research suggests that kefir may help promote a more balanced oral environment, particularly by limiting certain bacteria involved in cavity formation, such as Streptococcus mutans. Obviously, kefir is no substitute for brushing, fluoride use, or regular dental checkups. Its potential benefit lies more in its role as a fermented food that can complement good oral hygiene. This is provided that you choose a low-sugar kefir, especially when it is made with sugar water and fruit ^8,9.

Does kefir affect the gut-brain axis? 

Like other fermented foods, kefir has attracted scientific interest for its potential effects on the gut-brain axis—the constant communication between our microbiota, our immune system, and our brain. By altering certain gut bacteria and promoting the production of metabolites such as short-chain fatty acids, kefir could help create a less inflammatory environment, that may be conducive to healthy cognitive function.

Researchers are investigating its potential benefits for Alzheimer's disease, with encouraging results regarding inflammation, oxidative stress, and certain mechanisms linked to the toxic accumulation of proteins in the brain. However, this research is still in its very early stages, often conducted on animal or experimental models, and does not yet allow us to conclude that there are direct benefits for humans.

Milk kefir also provides nutrients that contribute to the normal functioning of the nervous system, such as certain B vitamins, choline, and folic acid. However, this research is still in its early stages, and while this fermented beverage remains a valuable part of a balanced diet, further research will be needed before kefir can be considered as a complementary treatment for Alzheimer’s and Parkinson’s diseases ^10,11,12,13 . 

Is kefir a real “coach” for athletes? 

Kefir may also have a role to play in sports nutrition. Whether made from cow’s, buffalo’s, donkey’s, or sheep’s milk, fermentation can alter the milk’s protein content, enrich it with bioactive peptides, and enhance certain antioxidant properties. Early findings in athletes are encouraging.
A study conducted among professional female soccer players suggests that daily consumption of kefir (200 mL per day) could modulate the gut microbiota—by increasing the levels of Akkermansia muciniphila and Faecalibacterium prausnitzii, which are bacteria often linked to short-chain fatty acid production and anti-inflammatory activity—and improve indicators of athletic performance. Studies in mice have also shown a potential effect on post-exercise fatigue.
While the evidence is still limited, kefir can be a good addition to a balanced diet that includes other fermented foods, fruits, and vegetables, as well as unsweetened beverages ^14,15,16.

Kefir checks a lot of boxes: a long history, a rich microbial diversity, compounds derived from fermentation, and a potential effect on the gut and oral microbiota. It shows promising results on certain metabolic, immune, cognitive, and athletic markers, but many of these findings need to be confirmed in humans. The right tactic? Enjoy it as a healthy fermented food that isn't too sweet, in reasonable amounts—for example, 100 to 200 mL a day to start.

To put it simply, kefir is not a miracle elixir. But when incorporated into a varied diet, along with sleep, physical activity, and a healthy lifestyle, it can become a simple and natural ally for your gut microbiota!