Is kombucha a miracle drink?
The real answer is that we don't really know yet. And that's where it gets interesting.
There's something a bit dizzying about the kombucha market: millions of bottles sold, claims everywhere, and as of 2023, not a single randomized controlled clinical trial on humans. Kombucha has been consumed for over 2,000 years, but science has long been content to observe mice. In 2023, a team from the University of Sydney published the first trial of its kind.
What science has finally confirmed in humans
The most concrete finding to date concerns blood sugar levels. In this Australian study published in Frontiers in Nutrition, participants consumed a high glycaemic index meal accompanied by either sparkling water, diet soda, or live kombucha. The result: the glycaemic index of the meal dropped from 86 with sparkling water to 68 with kombucha a clinically significant reduction that neither water nor diet soda produced. (1)
The following year, a Georgetown University study tested kombucha on people with type 2 diabetes the first of its kind in the world. In four weeks, without any change in diet, the average fasting blood sugar level dropped from 164 to 116 mg/dL in kombucha drinkers. For reference, the American Diabetes Association recommends a threshold of less than 130 mg/dL. The placebo group did not experience any significant change. (2)
This is a serious signal. Not definitive proof the trial only involved 12 people but a serious signal, with a double-blind protocol, a crossover design, and no declared financial conflicts of interest.
A genuinely less sweet alternative
This is probably the most immediate and tangible benefit. Fermentation consumes some of the initial sugar, resulting in a naturally low-sugar drink without the need for sweeteners. At Smile, we use less than 2.5g of sugar per 100ml. By comparison, a classic soft drink contains around 10g. It's not even in the same league.
What this means in practice: kombucha is a serious option for those who want to reduce their consumption of sugary drinks without giving up the pleasure of a tasty, sparkling drink. (3, 4)
The microbiome: the big misunderstanding in the organic aisle
This is the most widespread and misused argument. ‘Good for the microbiota.’ Perhaps. But recent studies call for much more precision and much more honesty about what we don't yet know.
The University of California San Diego study published in Scientific Reports in 2024 is the most rigorous on the subject to date: 24 participants, 8 weeks of follow-up, stool and blood analyses. Kombucha drinkers showed an increase in certain short-chain fatty acid-producing bacteria, compounds associated with gut health. However, the overall diversity of the microbiota decreased slightly. And inflammation markers remained unchanged. (5)
Another study, with a statistically robust protocol, found zero effect on the gut flora after three weeks of daily consumption. (6)
The most recent systematic review on the subject, published in 2025 in Fermentation, concludes that the best-documented benefits in humans relate to digestive comfort particularly in people suffering from irritable bowel syndrome with a tendency to constipation and that data on the microbiome remains promising but heterogeneous. (7)
What this means in practical terms: ‘improves your microbiota’ is a claim that science has not yet clearly validated. ‘Live fermented drink that can contribute to digestive comfort’, yes. It's not the same thing, and the nuance matters.
Live or pasteurised: the million-pound question (of good bacteria)
This is the angle that marketing carefully avoids, including ours until now.
Much of what is called ‘kombucha’ in supermarkets is pasteurised. It is heated to stabilise the taste, extend shelf life and simplify logistics. The result: the live microorganisms are eliminated. What remains is a tangy drink with interesting organic compounds, but without the active cultures that are the subject of all the studies mentioned above.
Clinical trials on blood sugar and the microbiome have all used live, unpasteurised kombucha. There are no regulations requiring manufacturers to clearly indicate this on the label. A simple clue: if it's not in the fridge, it's almost certainly pasteurised.
At Smile, our kombucha is unpasteurised. It must be kept cool because it is still alive - which is exactly what is needed for the interesting things to happen.
So, miracle or scam?
Neither. Live kombucha is a low-sugar fermented drink (like Smile), with encouraging signs for blood sugar regulation and a documented digestive comfort profile. It is not a medicine, and anyone who tells you otherwise is trying to sell you something.
What is certain is that it is better than soda on just about every measurable criterion. And what interests us at Smile is telling you what science confirms. Not because it's more virtuous, but because it's more honest, and we believe you can tell the difference between a live drink and a pasteurised liquid masquerading as one.
The rest of the research will be interesting. We're following it.
Disclaimer:
Smile brews kombucha, not medical conclusions. This article summarises studies published in peer-reviewed journals – the links are there if you want to dig deeper. And if you have a specific health issue, your doctor remains your best resource. We take care of the SCOBYs.
Sources
(1) Higgins et al. (2023). Glycemic index and insulin index after a standard carbohydrate meal consumed with live kombucha. Frontiers in Nutrition.
(2) Mendelson et al. (2023). Kombucha tea as an anti-hyperglycemic agent in humans with diabetes. Frontiers in Nutrition. https://doi.org/10.3389/fnut.2023.1190248
(3) de Miranda, J. F. et al. (2022). Kombucha: A review of substrates, regulations, composition, and biological properties. Journal of Food Science. https://doi.org/10.1111/1750-3841.16029
(4) Bishop, P. et al. (2022). Kombucha: Biochemical and microbiological impacts on the chemical and flavor profile. Current Opinion in Food Science.
(5) Ecklu-Mensah et al. (2024). Modulating the human gut microbiome and health markers through kombucha consumption. Scientific Reports. https://doi.org/10.1038/s41598-024-80281-w
(6) Aulesa & Góngora (2024). Assessing Kombucha: A Systematic Review of Health Effects in Human. J CAM Res Progress.
(7) Fraiz et al. (2025). Benefits of Kombucha Consumption: A Systematic Review of Clinical Studies. Fermentation. https://www.mdpi.com/2311-5637/11/6/353
