Scientific studies on kombucha

What does science say — and what does it not yet say — about kombucha? The fermentation of tea with SCOBY generates live bacteria and yeasts, organic acids, and polyphenols. Dozens of studies have analysed these compounds, but it is important to read them rigorously: most of the evidence comes from in vitro and animal trials, and human research — although growing — is still limited. Here we summarise the findings by topic, indicating the level of evidence for each.

Gut microbiota: the first human trial

In 2024, one of the first clinical trials analysing the regular consumption of black tea kombucha for eight weeks in adults with and without obesity was published. The authors observed changes in the gut microbiota — an increase in bacteria associated with a healthier profile and a reduction in groups linked to obesity. This is a promising first step; more extensive and longer-term trials are needed to confirm it.

Source: Regular Consumption of Black Tea Kombucha Modulates the Gut Microbiota in Individuals with and without Obesity · The Journal of Nutrition (2024).

Blood glucose: the clearest metabolic effect to date

A double-blind, randomised, crossover pilot trial (Georgetown University, alongside the University of Nebraska-Lincoln and MedStar Health) studied adults with type 2 diabetes who drank 240 ml of kombucha or a placebo daily for four weeks. After the kombucha period, fasting glucose dropped from an average of 164 to 116 mg/dL; the placebo did not produce a statistically significant change. This is a small, preliminary study — the authors themselves call for larger trials — but it is, to date, the clearest metabolic effect published. It aligns with the underlying idea of this page: what matters is not only what kombucha provides, but also the sugary drink it replaces.

Source: Kombucha tea as an anti-hyperglycemic agent in humans with diabetes – a randomized controlled pilot investigation · Frontiers in Nutrition (2023).

Inflammation and metabolic health

A randomised controlled trial studied green tea kombucha in individuals with excess body weight. The authors reported effects on inflammation markers and on salivary microbiota — with fewer bacteria associated with cavities and gum problems — attributed to the polyphenols and organic acids generated during fermentation. Important: the study did not find weight loss on its own. kombucha does not cause weight loss; it complements habits.

Source: Green Tea Kombucha Impacts Inflammation and Salivary Microbiota in Individuals with Excess Body Weight: A Randomized Controlled Trial · Frontiers in Nutrition (2024).

Organic acids: the chemical engine of fermentation

If there is one thread connecting almost everything else on this page, it is organic acids. During fermentation, the bacteria and yeasts in the SCOBY transform the tea's sugar into a mixture of acids: acetic (the most abundant, with antimicrobial and antioxidant action), glucuronic, gluconic, lactic, and malic. This acidity gives kombucha its character, hinders the growth of undesirable microbes, and accompanies the tea's polyphenols.

Glucuronic acid has received special attention: in the laboratory, kombuchas with higher glucuronic content show greater antioxidant capacity, and this acid is associated in the literature with processes of hepatic detoxification, antioxidation, and anti-inflammation. It is also the best scientific reason to care for fermentation: the acid profile — and thus the beverage's potential — changes according to the process, the starting tea, and the time. It is not marketing; it is chemistry.

The honest nuance, the same as always: these antioxidant and detoxification effects are demonstrated in vitro, under laboratory conditions. They indicate potential and explain a plausible mechanism, not a proven clinical effect in people.

Sources: Enhancing Antioxidant Benefits of Kombucha Through Optimized Glucuronic Acid by Selected Symbiotic Fermentation Culture · Antioxidants (2024) · Functional metabolites and inhibitory efficacy of kombucha beverage on pathogenic bacteria, free radicals and inflammation · Scientific Reports (2025).

Bioactive compounds: polyphenols and antioxidant activity

In the laboratory, kombucha shows antioxidant, antimicrobial, and anti-inflammatory activity that varies according to the starting tea (green, white, or black). That made with green tea stands out for its antioxidant capacity. These compounds — the organic acids from the previous section, along with the tea's polyphenols — are generated and concentrated during fermentation. These are laboratory results: they indicate potential, not proven clinical effects in people.

Source: Functional metabolites and inhibitory efficacy of kombucha beverage on pathogenic bacteria, free radicals and inflammation · Scientific Reports (2025).

The gut-brain axis: why it matters to feed your microbiota well

Much of the interest in fermented foods comes from how the gut and brain communicate. Research — predominantly in animal models — describes that the microbiota dialogues with the brain via the vagus nerve and metabolites such as short-chain fatty acids, and that a balanced microbiome participates in satiety signals. kombucha does not act "on the brain": its role is indirect, as one of the sources that help nourish this microbiota. This is a developing field.

Sources: Gut microbiome regulates brain signals through the vagus nerve · A gut sense for a microbial pattern regulates feeding · Nature (2025).

What you stop drinking: fewer sugary soft drinks

Here the evidence is solid, and it's not about kombucha itself, but about what it replaces. A global study estimated that in 2020, sugary drinks were associated with 2.2 million new cases of type 2 diabetes and 1.2 million cases of cardiovascular disease. Swapping a soft drink for a low-sugar kombucha reduces that exposure. This is probably the most robust argument in favour of keeping it in the fridge.

Source: Burdens of type 2 diabetes and cardiovascular disease attributable to sugar-sweetened beverages in 184 countries · Nature Medicine (2024).

An overview: what reviews conclude

When all human clinical trials published to date — eight in total, ranging from ten days to ten weeks in duration — are considered, the picture is as we have been describing: kombucha modestly modulates the gut and salivary microbiota and metabolic profile, with a more visible benefit in gastrointestinal symptoms. The reviewers' conclusion is cautious and one we endorse: there are promising signs, but human evidence is still scarce, and larger, longer studies are needed.

Source: Benefits of Kombucha Consumption: A Systematic Review of Clinical Trials Focused on Microbiota and Metabolic Health · Fermentation (2025).

What science does NOT yet state

For transparency, we state it clearly:

• It is not a medicine and does not cure or prevent diseases. No serious study supports this.
• It does not cause weight loss on its own. Human trials do not show weight loss attributable to the drink.
• It does not lower cholesterol (in people). Although lipid reductions have been observed in animals, human trials have not found significant effects on cholesterol or triglycerides. What is read in some industry blogs is ahead of the evidence.
• Human evidence is still limited. The most recent systematic reviews conclude that most findings come from in vitro and animal studies, and that more and better clinical trials are needed.
• Quality depends on the process and sugar content. A poorly fermented or very sugary kombucha does not provide the same benefits. That is why we control fermentation and reduce sugar to a minimum since 2015.

We prefer an honest drink to an exaggerated promise. kombucha is live fermented tea: a good substitute for soft drinks and a source of microorganisms and fermentation compounds. No more, no less.

References

1. Black Tea Kombucha and gut microbiota in obesity — The Journal of Nutrition (2024). Link
2. Kombucha tea as an anti-hyperglycemic agent in humans with diabetes (pilot RCT) — Frontiers in Nutrition (2023). Link
3. Green Tea Kombucha, inflammation and salivary microbiota (RCT) — Frontiers in Nutrition (2024). Link
4. Enhancing Antioxidant Benefits of Kombucha Through Optimized Glucuronic Acid — Antioxidants (2024). Link
5. Functional metabolites and inhibitory efficacy of kombucha — Scientific Reports (2025). Link
6. Sugar-sweetened beverages, diabetes and cardiovascular disease — Nature Medicine (2024). Link
7. Gut microbiome and the vagus nerve / feeding signals — Nature (2025). Link
8. Benefits of Kombucha Consumption: A Systematic Review of Clinical Trials — Fermentation (2025). Link
9. Kapp JM, Sumner W. Kombucha: a systematic review of the empirical evidence of human health benefit. Annals of Epidemiology (2019).
10. Villarreal-Soto SA et al. Understanding Kombucha Tea Fermentation: A Review. Journal of Food Science (2018).