People with Type 2 diabetes who drank the fermented tea drink kombucha for four weeks had lower fasting blood glucose levels compared to when they consumed a similar-tasting placebo beverage, according to results from a pilot study from Georgetown University's School of Health, the University of Nebraska-Lincoln and MedStar Health.
This finding points to the potential for a dietary intervention that could help lower blood sugar levels in people with diabetes and also establishes the basis for a larger trial to confirm and expand upon these results.
What is kombucha?
Kombucha, which was consumed as early as 200 B.C. in China, is made by fermenting sweetened black or green tea with a SCOBY, an acronym for symbiotic colony of bacteria and yeast. During fermentation the yeast converts the sugar into ethanol (alcohol) and acetic acid, the compound that gives vinegar its characteristic taste.
The end product is a little fizzy and tastes slightly sweet and slightly sour. You can buy it flavoured with fruit, ginger, rosemary, turmeric, rose petals, elderberries, lemongrass, maple, and so on.
Kombucha contains polyphenols, antioxidants that naturally occur in tea, and B vitamins. Commercial products contain less than 0.5 per cent alcohol by volume and typically have 30 to 35 calories per one cup serving, mainly from sugar, considerably less than sugar-sweetened soft drinks.
About the study
The crossover design had one group of people drinking about eight ounces (250 ml) of kombucha or placebo beverage daily for four weeks. Then after a two-month period to 'wash out' the biological effects of the beverages, the kombucha and placebo were swapped between groups with another four weeks of drinking the beverages.
Neither group was told which drink they were receiving at the time.
The findings
Kombucha appeared to lower average fasting blood glucose levels after four weeks from 164 to 116 mg/dL (9.1 to 6.4 mmol/L) while the difference after four weeks with the placebo was not statistically significant.
Guidelines from the American Diabetes Association recommended blood sugar levels before meals should be between 70 to 130 mg/dL (4.0 to 7.0 mmol/L).
The researchers also looked at the makeup of fermenting micro-organisms in kombucha to determine which ingredients might be the most active.
They found that the beverage was mainly comprised of lactic acid bacteria, acetic acid bacteria and a form of yeast called Dekkera, with each microbe present in about equal measure; the finding was confirmed with RNA gene sequencing.
The kombucha used in this study was produced by Craft Kombucha, a commercial manufacturer in the Washington, DC area. It has been re-branded as Brindle Boxer Kombucha.
"Different studies of different brands of kombucha by different manufacturers reveal slightly different microbial mixtures and abundances," says Robert Hutkins, Ph.D., University of Nebraska-Lincoln and the study's senior author. "However, the major bacteria and yeasts are highly reproducible and likely to be functionally similar between brands and batches, which was reassuring for our trial."
The researchers hope that a much larger trial, using the lessons we learned in this trial, could be undertaken to give a more definitive answer to the effectiveness of kombucha in reducing blood glucose levels in Type 2 diabetes.
Source: Frontiers in Nutrition, August 1, 2023.
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