Kombucha: marketing hype or scientific claims?

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.