Bacteria capable of disarming allergens

In mice, researchers¹ observed that the presence of gut bacteria changes how the body responds to peanuts. The group of mice with rich and diverse gut microbiota broke down the two proteins responsible for most allergic reactions, Ara h 1 and Ara h 2, far more effectively than mice raised with little or no gut microbiota. As a result, fewer intact allergens entered the bloodstream and the allergic reaction triggered after exposure was significantly less intense. Conversely, a second group with limited microbial diversity showed more markers of a severe reaction. 

The bacterial genus Rothia stood out in this research. It is naturally present in the human mouth and small intestine. In the laboratory, it breaks down the two main peanut allergens at specific sites, preventing IgE antibodies from recognizing them. Less recognition means less activation of mast cells, the immune cells responsible for allergy symptoms.

Some Staphylococcus strains have a similar effect, but not all of them. The study shows that two strains of the same species can behave in opposite ways, with one efficiently breaking down the allergen and the other not at all. 

A finding confirmed in patients with allergies

The researchers then analyzed saliva samples from 19 patients with peanut allergy. These children, ages 1 to 14, were studied before starting oral immunotherapy treatment. The group of patients that tolerated the highest allergen doses during controlled tests harbored more bacteria capable of breaking down peanuts, including bacteria from the Rothia genus, regardless of their blood levels of Ara h 2-specific IgE. They therefore showed greater allergy tolerance. This observation was then identified in 120 children monitored in an independent study, further strengthening its credibility.

More than 70% of peanut allergies persist over time. This makes the search for new ways to limit the severity of accidental allergic reactions particularly valuable. For affected children and their families, the goal would be to reduce the risk associated with unintentional exposure.These findings still need confirmation through larger studies before any clinical application, but they open up a serious avenue: a microbiota that protects or, conversely, increases exposure depending on the microorganisms it contains. A promising discovery for potential future treatments.

United States, India…
Pickles: the ancient art of fermented vegetables

For many people, the word “pickles” conjures up images of tangy, vinegar-soaked cucumbers that are a staple of American hamburgers. The exact origin of pickles remains unclear, but as early as 2030 B.C., cucumbers from the Indian subcontinent were reportedly being preserved through fermentation.¹ And the tradition is still very much alive. In India, pickled vegetables and fruits—such as mangoes, lemons, and chili peppers—known as achar, play an important role in Indian cuisine.¹ But be aware: not all pickles are created equal. Traditional pickles are left to ferment for several months in a very salty brine—a low-oxygen environment conducive to fermentation by lactic acid bacteria—while other, speedier recipes combine fermentation with vinegar. “Refrigerated” pickles, on the other hand, ferment for only a few days and must be kept cold.²
Long-fermented varieties have greater nutritional benefits as they contain more live microorganisms, some of which may contribute to the balance of the gut microbiota, digestion, and even immunity, although these health effects have yet to be confirmed.^3–5

Sweden
Surströmming: canned fermented herring

This Swedish specialty is made from fresh herring that is salted and then submerged in brine where fermentation continues inside the can.⁶ As the process unfolds, the can naturally begins to bulge. The health benefits of this surprising dish—which has a very sour and slightly fizzy taste—⁶ are thought to come primarily from the fish itself, which is rich in protein and omega-3 fatty acids.⁷ Fermented fish in general has also been associated with possible antioxidant and antihypertensive effects, as well as potential protection against certain cancers and beneficial changes to the gut microbiota (increase in Bacteroidetes, decrease in Firmicutes).⁸ 
But, these benefits should be taken with a grain of salt, as there is far from a consensus on them: in one human trial, volunteers consuming surströmming for a week experienced no significant changes to their gut microbiota.⁹ 

Morocco, Algeria
Smen: a long-lasting butter

Smen is a fermented, clarified⁽¹⁾ butter traditionally made in North Africa. It is prepared from camel milk: after the milk undergoes spontaneous fermentation, the butter is separated by churning, then fermented, salted, and stored in hermetically sealed earthenware jars, where it can age for several years.¹² Over time, smen develops an intensely rich flavor and powerful aromas. As with all fermented dairy products, fermentation is thought to produce small bioactive molecules that have beneficial effects on health. However, many of the health benefits traditionally attributed to smen—from treating hemorrhoids and rheumatism to soothing colds and burns—belong more to cultural tradition than to firmly established science.¹³ Nevertheless, antibacterial properties against Staphylococcus aureus and Escherichia coli have been demonstrated in vitro, and accelerated wound healing has been observed in animals (but not—yet?—in humans).<sup>14

(1)</sup> Clarification involves removing water and milk proteins (particularly casein), leaving almost nothing but fat and giving it a much longer shelf life.¹²

Bulgaria
Yogurt: for better milk digestion

Yogurt is a fermented dairy product made using two specific bacteria: Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus.¹⁰ These bacteria convert the lactose—the natural sugar in milk—into lactic acid. This process gives yogurt its characteristic taste and texture, while also making the milk easier to digest. Other bacteria can ferment milk too, but the resulting product is then referred to as “fermented milk” rather than “yogurt”. One direct result of this lactic fermentation process is that it can make dairy easier to digest for people with lactose intolerance.¹⁰ The consumption of yogurt and other fermented dairy products has also been associated with a reduced risk of breast and colorectal cancer and type 2 diabetes mellitus, better weight management, and improved cardiovascular, bone, and digestive health.^10,11 
But here again, a little caution is needed: while the associations are promising, science is still far from proving a direct cause-and-effect relationship.

Ethiopia
Injera: a gluten-free flatbread 

Injera is a traditional fermented flatbread from Ethiopia, made from teff flour,¹⁵ an ancient gluten-free grain. A staple of Ethiopian cuisine, it is particularly rich in carbohydrates, while also providing protein, fiber, and a range of minerals. Its fermentation is powered by yeasts—notably the well-known brewer’s yeast Saccharomyces cerevisiae—and lactic acid bacteria.^16–19 Their action appears to improve protein digestibility, increase the activity of beneficial compounds such as phenols, and enhance antioxidant activity.^15,20
It can also reduce compounds (known as antinutritional factors) naturally present in grains, which limit the absorption of certain nutrients.²¹

Nigeria
Gari: an affordable cassava-based food

Gari is a grainy, creamy flour made by roasting fermented cassava paste.²² This staple food is part of the daily diet of millions of Nigerians thanks to its availability and affordability. The traditional production process involves several sequential steps: grating the cassava, optionally adding red palm oil, fermenting, draining (dehydration), sifting, roasting on a heated griddle to gelatinize the starch, and then cooling.²² All these steps help reduce certain undesirable compounds such as cyanide, but also destroy vitamins. Gari is rich in carbohydrates and fiber but low in protein. It may also contain phenols with antioxidant properties, although this depends on how the gari is made and the type of cassava used.²³

Indonesia
Tempeh: taking the nutritional benefits of soy to the next level

Originating on the island of Java, tempeh is an Indonesian staple that has become a favorite among vegetarians around the world. This fermented soy product, far less bland than its cousin tofu, adds nutty and mushroom-like flavors to many Indonesian dishes. It is made by fermenting soybeans with the fungus Rhizopus oligosporus, a technique said to have been inspired by traditional Chinese methods of making soy sauce.²⁴ This fermentation process improves the absorption of soy’s proteins, minerals, vitamins, and isoflavones, while reducing antinutritional factors. The result is a product of high nutritional quality that can contribute to preventing malnutrition.^24,25 Some authors have also reported potential benefits ranging from lower LDL cholesterol and blood pressure²⁶ to antioxidant, digestive, and cognitive effects—²⁴ and even improved athletic performance.²⁷ However, most of these findings are still very much preliminary. 

Philippines
Bagoong: a condiment rich in protein… but also in salt and histamines

Bagoong is a traditional Filipino condiment made from fish or small shrimp that are ground and fermented with salt. Although rich in protein, the nutritional composition of this paste varies depending on the recipe.^28,29 For example, shrimp-based bagoong (also known by the generic names Terasi in Asia, Belacan in Malaysia, and Kapi in Thailand…) tends to be slightly higher in fat and lower in minerals. As for its potential health benefits (antioxidant? cholesterol-lowering?),³⁰ they have rarely been studied, and often only in test tubes rather than in humans, which makes the results highly uncertain. Keep in mind that bagoong is high in both histamines (with a risk of poisoning sometimes called non-allergic food hypersensitivity) and in salt (an ingredient best consumed in moderation).^28,29,31 

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Miso is a traditional Japanese condiment and one of the hallmarks of umami,¹ the fifth basic taste alongside sweet, salty, sour, and bitter. In the Land of the Rising Sun, it is best known as the star ingredient of the famous soup that bears its name.¹ Since the 1970s, it has steadily made its way into Western kitchens, where it is used as a versatile condiment.² 

What is miso?

Miso is a fermented soybean paste produced in two stages:^1,2 

• koji preparation: an initial substrate (usually rice, barley, or soybeans) is inoculated with a microscopic filamentous fungus—most commonly Aspergillus oryzae. This produces what is known as ‘koji’.
• final fermentation: the koji is then mixed with a puree of cooked soybeans and salt. This mixture undergoes a second fermentation, this time involving yeasts and bacteria (including lactic acid bacteria). This stage can last anywhere from a few weeks to three years.

There are four main categories of miso based on its ingredients: rice miso (which accounts for around 80% of production in Japan), barley miso, soybean miso, and blended miso.^1,2 Its flavor (ranging from sweet to salty) and color (white, red, or black) depend on the ingredients used, the proportion of koji, and how long it is left to ferment.^1,2 

Health benefits of soy

Miso, whose main ingredient is soy, retains many of soy’s nutritional benefits. Soy is rich in high-quality protein (twice as much as most other legumes) because it contains all nine essential amino acids.^3,4 Soy is also rich in fiber, which helps feed our gut bacteria, and in minerals. Miso also contains isoflavones, plant compounds that can bind to human estrogen receptors. These are sometimes referred to as phytoestrogens. 

This has raised concerns:⁵ could these compounds affect hormone-dependent cancers, fertility, or hormonal development? While these concerns were once legitimate, current evidence is entirely reassuring: research has found no increased risk and even suggests that soy consumption may have a potential protective effect against cancer,⁶particularly in women.^7,8

One final point to keep in mind: miso, like any soy-based food, contains several allergenic proteins.⁹ Although fermentation can significantly reduce their allergenic potential by breaking down complex proteins, the risk remains for people with a high sensitivity to soy.⁹ 

Fermentation that boosts health benefits

Miso’s double-fermentation process transforms soybeans into a food that is not only easier to digest but also richer in bioactive compounds.^3,9,10 For example, fermentation improves the digestibility of soy proteins by breaking them down into smaller molecules that are easier to absorb.³ It also increases the bioactivity of the well-known isoflavones, transforming them into a form of phytoestrogens that is more bioavailable and active in the body, with potential health benefits, including :

• protection against certain cancers,
• improved lipid profile,
• and beneficial effects on cardiovascular health—although the evidence remains inconclusive.^3,10–12 

It should be noted, however, that because these compounds have estrogen-like activity, consuming them in excessively high amounts could potentially pose toxic risks to the reproductive system, particularly in pregnant women, women of childbearing age, and prepubescent children (ANSES, French National Agency for Food, Environmental and Occupational Health & Safety).¹³
Miso is naturally rich in diverse and varied microorganisms, including the trio Aspergillus oryzae derived from koji), the yeast Zygosaccharomyces rouxii and the bacterium Tetragenococcus halophilus.^1,2,14 This microbial community enriches the gut microbiota,¹⁵ promoting its diversity and stability, boosting certain beneficial bacteria while reducing less favorable ones. This rebalancing of the microbiota is intriguing enough that some researchers have suggested a potential protective effect against diabetes mellitus—^10,15 but for now, that hypothesis still needs to be substantiated. 

Finally, an improved gut flora means an increased production of key compounds, particularly 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. )  (SCFAs).¹⁵
These small molecules work in our favor: they nourish the cells of our colon, help strengthen our intestinal barrier, support immune function, and may help reduce inflammation.^4,9,15  

The salt paradox

The WHO and public health campaigns regularly remind us: we should cut back on salt. Yet miso is one of the main sources of salt in the Japanese diet. And here comes the paradox: despite its high salt content, this Japanese specialty does not seem to have the same harmful effects as plain old salt: consuming it may have no effect on blood pressure.^2,16,17 It may even lower heart rate¹⁶and increase salt excretion through urine!¹⁸ 
How can this surprising result be explained? One possibility is potassium. Soybeans and the other ingredients commonly found in miso soup (vegetables, fish...) are rich in potassium, which may help counteract some of salt’s blood-pressure-raising effects.¹ According to some experts, the key may therefore be not just how much sodium we consume, but the balance between sodium and potassium.^1,2,19

Thus, thanks to its double fermentation process, miso becomes easier to digest and richer in potentially beneficial compounds. When consumed in moderation—high daily intake of 1 to 5 bowls per day appears to be associated with an increased risk of stomach cancer in men–⁷ it may offer a range of health benefits, despite its high salt content.

Check out our series of articles on microbiota and fermented foods:

Kimchi is a traditional Korean side dish, typically made from cabbage or radishes depending on the recipe.^1–3 
Historically, it was prepared in winter using lacto-fermentation—a clever way to preserve vegetables for long periods.⁴ The cabbage is soaked in brine (a mixture of water and salt) for several weeks, allowing lactic acid bacteria to multiply. By producing lactic acid, these bacteria give kimchi its tangy flavor while naturally preserving it.⁵ 
It shares a resemblance with European sauerkraut—salted, fermented cabbage—though the type of cabbage and spices used are quite different.⁶ Kimchi is so deeply woven into Korean culture that Kimjang—the communal tradition of preparing vast quantities of kimchi for the winter—was inscribed on UNESCO’s List of Intangible Cultural Heritage of Humanity in 2013. 

Cabbage + fermentation = a plateful of health benefits

Since it’s made from cabbage, kimchi is low in calories (18 kcal/100g) and rich in beneficial fiber. It also contains a range of compounds characteristic of the Brassicaceae family (the large family that includes cabbage, turnips, radishes, and mustard), whose health benefits may be almost as impressive as their tongue-twisting¹⁽¹⁾ names.^2,4
Kimchi also provides several vitamins—notably A, C, B1, and B2— as well as minerals—calcium, potassium, iron, and phosphorus.^2,4
The health benefits of this Korean dish do not come from cabbage alone, they may also be attributed to the fermentation of the cabbage⁶ : compared to fresh cabbage, kimchi (fermented cabbage) has been associated with reductions in blood pressure, body fat, fasting blood sugar and total cholesterol… although these findings should be taken with a pinch of salt: the study involved only 22 people.⁸ 
Fermentation also enriches kimchi with live lactic acid bacteria, notably the genera Lactobacillus, Leuconostoc and Weissella , along with the valuable metabolites they produce.^2,4,5,7
For example, eating kimchi appears to be associated with an increase in gut bacteria known for producing 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 recognized for their beneficial effects on gut health and metabolism—and with a reduction in far less desirable bacteria, such as Clostridium and Escherichia coli.⁹ 
More beneficial bacteria, fewer potentially harmful bacteria: kimchi may just be a tasty ally of your gut microbiota . 

Caution: effects… and dosage matter!

Given this promising nutritional profile, some researchers have explored the potential links between kimchi consumption and a surprisingly wide range of health outcomes, from obesity, cancer, atopic dermatitis, irritable bowel syndrome, and even cardiovascular health and skin health … ^{3,6,7,10–14}
A few studies have been conducted, but they remain scarce and are often limited to Asian populations. In short, a little caution is warranted when interpreting the results, which remain inconclusive, and even when an effect is observed, it tends to be fairly modest.

For example, with regard to obesity, some studies suggest that kimchi consumption may be associated with a potential beneficial effect. One large study that followed 115,726 Koreans found that moderate kimchi consumption—1 to 3 servings per day (perfectly common in Korea, perhaps a little ambitious for the average Westerner)—was associated with a lower prevalence of obesity, particularly among men. But caution: this does not mean there is a cause-and-effect relationship. Kimchi lovers may simply be Koreans who tend to lead healthier lifestyles overall.¹
Nevertheless, another study—this time involving 3 grams of powdered kimchi daily (versus a placebo)—seems to support a potential role for kimchi in weight management.¹⁵ Let’s also put this “discovery” into perspective: eating more vegetables has been linked to better weight management for quite some time… 
Of course, as with most things in nutrition, more is not necessarily better: beyond a certain level of consumption, any potential benefits may diminish, because kimchi, due to its recipe, contains a lot of salt, which can contribute to high blood pressure and is a risk factor for stomach cancer.^1,2,16 

Check out our series of articles on microbiota and fermented foods:

Kombucha is a non-alcoholic or low alcohol fermented tea-based beverage said to have originated in China around 220 B.C ¹. It is prepared using a mixture of bacteria and yeast, which form a “mother” (similar to the process used to make vinegar) that is added to a sugary tea-based solution . In recent years, the drink has been embraced by celebrities, influencers, and marketing gurus, making it popular in Western countries, where it is credited with a wide range of health benefits ^1,2.
But what does the science actually say? What health effects have been definitively proven? Should the influencers’ claims or the health promises on certain labels be taken at face value? 

Why all the hype? 

Science has shown that diet strongly influences the composition and function of our gut microbiota, with potential knock-on effects on the body’s functioning and health ². There is therefore growing interest in fermented foods in general due to their bioactive compounds and potential benefits. Kombucha is no exception. With its variety of surprisingly tangy flavors, the drink’s reputation is boosted by folklore describing it as the “tea of immortality” ¹. However, there remains concern that the influencers and marketers may have jumped the gun a bit, since the results of studies are far from conclusive. 

Results in humans remain inconclusive 

Some studies conducted on animal models do suggest that consuming the fermented tea may confer health benefits ²: these include antihyperglycemic effects (which limit harmful spikes in blood sugar levels), antioxidant effects (which protect cells from oxidation), and anti-inflammatory effects, as well as changes in the gut microbiota (increased lactobacilli) associated with improved metabolic health. But these results were obtained in animals, not in humans. 

So, what about humans? Intervention studies involving kombucha are few, small in scale, and therefore not very robust. A small number of trials suggest: 

• a beneficial effect on blood glucose levels: a smaller rise in blood glucose levels after a meal in healthy subjects ³, and a decrease in blood glucose levels in people with diabetes ⁴. However, another trial found no changes in these parameters, nor in inflammatory markers ²; 
• a beneficial effect on the gut microbiota of people of normal weight ^2,5 and obese individuals ⁵, with more pronounced effects in the latter group ⁵ ;
• an improvement in gastrointestinal symptoms in overweight individuals (green tea kombucha consumed as part of a healthy, low-calorie diet) ⁶, and in constipation in people with irritable bowel syndrome (beverage rich in fiber and vitamins) ⁷. 

So, what does this tell us? In 2025, a team set out to compile all the results published to date, a total of 8 clinical trials ⁸. The verdict? Kombucha may have modest beneficial effects on digestive health and the gut microbiota in some people, as well as on certain biological markers. However, the results are highly inconsistent, and the sample sizes are small, which does not allow for robust conclusions about clinical benefits. Caution is therefore advised... 

What mechanisms are involved? 

If the health effects are confirmed, what mechanisms could be involved? On the one hand, tea infusions provide potentially beneficial molecules, depending on the type consumed. For example, green tea is rich in catechins ⁸, molecules which reduce oxidative stress. At the same time, kombucha’s preparation method makes it a source of bacteria (particularly acetic and lactic acid bacteria) and yeasts ^2,8. These microorganisms are capable of producing a wide variety of metabolites with potential health benefits ^2,8 including:

• phenolic compounds,
• organic acids, 
• vitamins, and more.  

But that’s not all. Consuming the fermented tea may be associated with an increase in our gut microbiota of bacteria that produce 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. )  (SCFAs) such as butyrate, acetate, and propionate ^2,8. These small fatty acids can enter our bloodstream and are considered particularly beneficial for our gut barrier, ​​​​metabolism and immune system ⁸. 
Among the species that produce SCFAs, one appears to be specifically associated with kombucha: Weizmannia coagulans (formerly known as Bacillus coagulans), which is thought to colonize, at least temporarily, the gut of those who consume it ². Bacteria involved in the metabolism of polyphenols, such as Ellagibacter isourolithinifaciens,  are also thought to have a stronger presence​​​​​​​ ². 
​​​​​​​Again, though, these tentative findings are based on very preliminary research.  

Finally, a few notes of caution 

Kombucha is generally considered safe to drink. However, variability in the microbial composition of “homemade” versions, hygiene practices, and the associated contamination risks are key concerns that require close attention. A few isolated case studies have reported adverse events following prolonged daily consumption, such as nausea, vomiting, or headache ⁹. Furthermore, ethanol production during fermentation is not negligible. Therefore, caution is advised for pregnant women, young children, immunocompromised individuals, or those with renal failure ⁹. 

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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!

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Infertility affects approximately 1 in 10 couples. But a new discovery ¹ could bring them hope: the tiny bacteria that live in our bodies may play a key role in our ability to conceive. These communities interact with our immune system, our hormones, and our metabolism.

For women and men: a matter of balance

In women, a healthy vaginal microbiota is dominated by beneficial bacteria called Lactobacillus, particularly the species L. crispatus. These bacteria are allies of our intimate health by maintaining an acidic environment, limiting inflammation, and promoting the uterus’s receptivity to pregnancy. When this balance is disrupted (vaginal dysbiosis), other bacteria associated with an imbalance become more abundant: the vaginal pH rises, inflammation increases, potentially impairing sperm motility, embryo implantation and immune tolerance between the mother and the fetus.

The uterus is also believed to have its own microbiota. The presence of beneficial bacteria in the endometrium is thought to improve pregnancy rates, while certain pathogens are thought to reduce them. However, these findings remain controversial, because the samples are difficult to analyze and are highly susceptible to contamination.

In men, semen also contains its own microbiota. When beneficial bacteria dominate, they produce fewer inflammatory compounds and protect spermatic DNA. Conversely, certain pathogenic bacteria may increase inflammation and slow sperm motility. However, studies linking seminal microbiota to male fertility are still limited and require further research.

The gut: the hidden conductor?

The gut microbiota may also influence fertility through the immune system, hormones, and metabolism. In women with polyendocrine ovarian metabolic syndrome (formerly polycystic ovary syndrome), an imbalance in the gut microbiota seems to promote inflammation, insulin resistance, and hormonal disruptions. Another example is endometriosis, a condition associated with gut dysbiosis that may also alter estrogen metabolism, enhance inflammation, and contribute to the growth of lesions which could potentially affect the embryo’s ability to implant in the uterus.

How can balance be restored?

As a preventive measure, it is important to avoid any practices that may disrupt your vaginal or seminal microbiota and your gut microbiota. In the event of a confirmed bacterial infection (vaginosis), your doctor may prescribe appropriate treatment.
Approaches aimed at modulating microbiota to restore balance – such as probiotics – are also being investigated, but their impact on pregnancy outcomes remain uncertain. As for microbiota transplantations, they are still limited to clinical research. In the future, microbiota profiling could help better personalize care for couples undergoing assisted reproductive technology (ART) cycles. However, this approach remains under evaluation and requires more robust scientific evidence before it can be incorporated into standard clinical practice.

Although fermented milk products have existed for millennia—as evidenced by traces of lactic fermentation found in pottery dating back to 8000-7000 BC—it wasn’t until the early 20th century that Stamen Grigorov and Elie Metchnikoff identified a bacterium essential to yogurt production ¹.

Today, in most parts of the world, the term yogurt refers to a fermented milk product made through the combined action of two bacteria:

• Streptococcus thermophilus
• Lactobacillus bulgaricus.

These lactic acid bacteria work in symbiosis and are essential to yogurt production through the process of milk fermentation. It can be made from cow’s or sheep’s milk, plain or flavored, stirred or enriched with cream…
While recipes, spellings, textures, and pronunciations may differ, they all trace back to the Turkish root yoğurt, found in the verb “yoğurmak” meaning “to thicken”. Only skyr follows a slightly different tradition: originating in Norway and Iceland, it is a strained yogurt made from skim milk, with a denser texture. Very low in fat and particularly high in protein—about twice as much as regular yogurt—it has a particularly appealing nutritional profile ².

Beyond their differences, all of these yogurts share nutritional benefits worth exploring in more detail to better understand their effects on health, digestion, and microbiota.

They help make our gut a more hospitable place

The first benefit of yogurt is that it reshapes the population of microorganisms in our gut. This is because Streptococcus thermophilus and Lactobacillus bulgaricus are probiotics that help maintain the balance and diversity of the gut microbiota ^3,4.This diversity goes hand in hand with a healthy and well-functioning microbiota, which ensures good digestion and a stronger immune system.

They help protect us from minor colds

Thanks to the probiotics they contain, yogurts could help support the gut’s immune defenses. Their bacteria help maintain a balanced gut microbiota, limit the growth of certain unwanted microorganisms, and strengthen the intestinal lining. Some studies also suggest improved regulation of the immune response and a reduction in certain digestive infections, but these effects vary depending on the product consumed, the strains it contains, and the individual ^5,6.
As a result, regular yogurt consumption could help lower the risk of gastrointestinal infections… and even common colds in older adults! One study has found that consuming 90 g of yogurt daily boosts the immune system and protects against infections ⁷!

They help fight diabetes

For several years now, scientists have observed that regular consumption of dairy products—particularly plain yogurt (mainly made from cow’s milk, typically 80 to 125 g per day)—is associated with a lower risk of developing type 2 diabetes. According to the International Diabetes Federation, type 2 diabetes mellitus currently affects around 11% of the world's population. This protective effect may occur through the gut microbiota, regardless of whether the yogurt is high-fat or low-fat ^8,9.

They help shed excess weight

Regular yogurt consumption has also been associated with less long-term weight gain compared with people who never eat yogurt ¹⁰. This may be partly explained by yogurt’s high protein content, which promotes satiety and helps better regulate appetite ¹¹.
Yogurt is also a good source of calcium—from milk—, which may play a role in metabolism. Some data suggest that calcium helps modulate the gut microbiota and strengthen the intestinal barrier, thereby limiting the inflammatory processes involved in obesity ¹².
Finally, results from the PREDIMED study indicate that daily yogurt consumption is also associated with lower abdominal obesity, further supporting the idea of a beneficial effect on body composition ¹³.

They help combat lactose intolerance

Yogurt is also a must-have for anyone dealing with lactose intolerance caused by cow’s milk. With fermentation, the bacterium Lactobacillus bulgaricus converts lactose into lactic acid, making it much easier to digest. This process helps restore the gut’s pH balance and reduces symptoms of digestive disorders such as constipation, bloating, and diarrhea, which can often cause abdominal pain ^14,15. Eat as much as you like—your digestive system will thank you!

They help keep our hearts healthy

Yogurt has another ace up its sleeve: it protects our cardiovascular system over the long term. Scientists have found that eating one to two yogurts a day reduces the risk of developing high blood pressure by 10% to 20% ¹⁶. They have reached similar conclusions regarding heart attacks and stroke-related mortality, specifically with whole-milk yogurt ^17,18.
 

They help us strengthen our bones

Daily yogurt consumption is associated with stronger bones, thanks to an increased bone density (+3 to 4%) and a reduced risk of osteoporosis (up to -39% in women and -52% in men) ¹⁹. These benefits seem to be linked to yogurt’s high calcium and protein content, and potentially its positive impact on the gut microbiota ^20,21.

Do they bring us closer to immortality?

Could yogurt actually extend our life expectancy? A study of a woman who lived to be 117 years old revealed a surprisingly “young” gut microbiota, associated with good overall health. Her regular consumption of yogurt may have contributed to the presence of beneficial bacteria such as Bifidobacterium ²².

More broadly, research shows that the microbiota plays a crucial role in aging by influencing immunity, inflammation, and overall health ²³. While these results are still preliminary and do not prove a direct link between yogurt and longevity… they’re still a good excuse to have another one, just in case science has a few more surprises in store for us!

Check out our series of articles on microbiota and fermented foods:

Infertility, whether affecting males or females, is a major global health concern, with an estimated prevalence of 8 to 12% of the population. Research ¹ on microbiota has provided new insights into reproductive health by identifying microbial communities that interact with the host at the metabolic, immune, and endocrine levels.

Key role of microbiota in the reproductive systems

In women, a vaginal microbiota dominated by Lactobacillus (particularly L. crispatus) is associated with an acidic pH, reduced inflammation, and an endometrium conducive to embryo implantation. Conversely, vaginal dysbiosis is associated with an elevated pH, increased production of pro-inflammatory metabolites, and impaired sperm motility, embryo implantation, and maternal-fetal immune tolerance. The endometrium is also thought to host a low-biomass microbiota. The presence of Lactobacillus is associated with improved reproductive outcomes (conception, implantation, clinical pregnancy, or live births), whereas Atopobium or Gardnerella are more frequently associated with failure.

In men, the seminal microbiota influences sperm quality: Lactobacillus is associated with lower production of oxidative compounds and better sperm DNA integrity, whereas Prevotella and Streptococcus are associated with inflammation and impaired sperm motility. However, evidence linking the seminal microbiota to male infertility is still emerging, as findings are often limited by small sample sizes and substantial inter-individual variability.

The gut microbiota is also involved

The gut microbiota may also influence fertility through immune, endocrine, and metabolic pathways. For example, in polyendocrine ovarian metabolic syndrome (formerly polycystic ovary syndrome), gut dysbiosis (characterized by reduced microbial diversity, increased Escherichia, decreased Lactobacillus) appears to promote inflammation, insulin resistance, and hormonal imbalances through the translocation of lipopolysaccharides (LPS) across the intestinal barrier and the disruption of intestinal enzymes. 

What mechanisms and interventions are involved?

The vaginal, uterine, intestinal, and seminal microbiota are thought to influence fertility through immuno-inflammatory and endocrine-metabolic mechanisms, as well as by maintaining a protective barrier effect.
Several approaches are being investigated to optimize microbiota prior to assisted reproductive technology (ART) treatments:

• antibiotics are effective for treating confirmed infections (chronic endometritis, vaginosis); some studies have reported improved clinical pregnancy rates following antibiotic treatment – sometimes doubling pregnancy rates in IVF – but antibiotic therapy also depletes beneficial Lactobacillus ;
• probiotics (oral or intravaginal) can partially restore microbial balance, although their effects on pregnancy outcomes remain inconsistent ;
• emerging therapies (fecal or vaginal transplantation) are promising but remain experimental and require well-controlled clinical trials.

Microbiota profiling could therefore become a valuable component of ART protocols by refining patient stratification and guiding targeted adjuvant therapies. However, before implementation, stronger causal evidence, validated biomarkers, and standardized methodological frameworks are required.

A common cancer among people over 50

Colorectal cancer affects the colon or rectum and is the second leading cause of cancer-related death worldwide, according to the WHO ¹.

This disease results from an abnormal transformation of colorectal cells that multiply uncontrollably.
Known risk factors include:

• age,
• family history,
• and certain inflammatory bowel diseases.

But researchers have begun to investigate another potential factor: bacteria present directly within tumor tissues. 

Bacteria at the heart of the tumor

It has long been established that the human gut is home to billions of microorganisms – the gut microbiota – which play a key role in immune system and overall health.

A study ³ published in Nature Communications in December 2025, involving 937 Swedish patients, found that bacteria are also present directly within tumor tissues, alongside colorectal cancer cells. 

Using an advanced sequencing technique, researchers identified 361 bacterial species in the tumors and adjacent tissues, including:

• several genera from the Enterobacteriaceae family (notably E. coli),
• several genera within the Firmicutes phylum,
• as well as the genera Fusobacterium, Akkermansia and Treponema.

The findings suggest that specific microbial profiles are associated with poorer clinical outcomes: for example, pks+ strains of E. coli were found in 17.4% of the tumors analyzed. These bacteria carry a genetic module –pks – which enables the production of colibactin, a toxin which directly attacks the DNA of colon cells.

The researchers also observed that some bacteria present inside tumors appear to interact with the local immune system by activating inflammatory pathways, a mechanism known to promote tumor progression.
These associations were consistently observed across multiple patient cohorts, which reinforces the reliability of the findings.

Promising results

Based on these observations, the researchers developed a risk score based on the bacterial composition of colorectal tumors.
This score can help predict how the disease is likely to progress in a patient, complementing existing diagnostic tools – regardless of :

• age,
• cancer stage,
• or the tumor’s genetic characteristics.

Ultimately, the bacterial profile of colorectal tumors could become a valuable tool to aid in prognosis and patient monitoring, and pave the way for new therapeutic strategies targeting the immune system and microbiota.
However, these results remain correlational and further studies are needed to confirm the underlying mechanisms.