Small randomized controlled trial finds kombucha decreased fasting blood glucose in individuals with type 2 diabetes

A recent study published in Frontiers in Nutrition evaluated the anti-hyperglycemic effects of kombucha tea in diabetic adults.

Diabetes mellitus, one of the leading causes of death worldwide, is a significant risk factor associated with kidney failure, peripheral vascular disease, coronary heart disease, reduced quality of life, and stroke. Diabetes rates have increased by over 400% in the last three decades. The high prevalence of diabetes in the United States (US) and various countries has prompted a search for dietary strategies that may lower the disease burden.

Kombucha is a beverage produced by fermenting sweetened tea. Despite the historically suggested health benefits of kombucha, only one study has evaluated its health benefits in humans. Nevertheless, numerous studies have been conducted in animal models. Building upon the evidence from animal studies, the authors speculated that kombucha could reduce blood glucose levels in diabetic individuals.

About the study

The present study evaluated kombucha as an anti-hyperglycemic agent in adults with type 2 diabetes (T2D). This double-blind, single-center, randomized, controlled cross-over trial was conducted in Washington, DC. Individuals were recruited from a primary care clinic between October and November 2019. Eligible participants were T2D patients aged 18 or above willing to measure their blood glucose levels daily.

Subjects were excluded if they were allergic to kombucha or its ingredients. In the first intervention arm, participants consumed one of the study drinks (kombucha and placebo) with dinner for four weeks. In the second intervention arm, which commenced after eight weeks of washout, participants consumed the alternate drink for another four weeks. Subjects measured their fasting blood glucose levels every day and reported weekly. Placebo was an unfermented sparkling drink.

Kombucha was prepared through traditional fermentation with a symbiotic consortium of bacteria and yeasts. The primary outcome was the mean fasting blood glucose levels. Secondary outcomes included self-reported outcomes on a questionnaire about overall health, gut health, vulvovaginal health, mental health, skin health, and insulin requirement. Additionally, chemical and microbial analyses of kombucha were performed.

Findings

The team recruited and randomized 28 participants; however, the final sample comprised 12 individuals after exclusions or voluntary withdrawals. Further, five participants had incomplete data; therefore, although 12 participants had questionnaire data, only seven were included in fasting blood glucose analyses. Participants were, on average, aged 57, and most (75%) were females.

Six individuals were White, and the remaining were African American. Kombucha significantly reduced the mean fasting glucose concentrations after four weeks relative to baseline. Placebo was not associated with lower levels relative to baseline. Notably, there were no significant differences in fasting blood glucose levels at four weeks between participants in kombucha and placebo groups.

When analyses were restricted to participants with baseline fasting blood glucose levels > 130 mg/dL, kombucha was associated with an average reduction of 74.3 mg/dL compared to a 15.9 mg/dL decrease with placebo relative to baseline levels, and this difference was statistically significant. Statistical analysis was not performed for secondary outcomes.

Microbiological analysis revealed that kombucha mainly contained lactic acid bacteria, acetic acid bacteria, and yeasts. Microbes were below the detection limit in the placebo. The researchers also performed 16S ribosomal ribonucleic acid (rRNA) sequencing. Most bacteria were Firmicutes, with several genera from the Lactobacillaceae family as the predominant members.

Most yeasts and fungi in kombucha were mainly from Dekkera and Sordariales. Kombucha contained acetic acid (1.06 g/L), lactic acid (0.26 g/L), and ethanol (11.9 g/L). Ethyl alcohol and organic acids were not detected in the placebo. Kombucha had a lower pH (3.52) and was slightly sourer than placebo (6.3).

Conclusions

In sum, the study demonstrated that a four-week kombucha intervention caused a significant decrease in fasting blood glucose levels in T2D subjects with elevated fasting blood glucose levels. Notably, two participants with well-controlled fasting blood glucose levels at baseline showed increased levels after kombucha intervention, which were still within the healthy range.

The study’s limitations include the small sample size and high attrition rate. Moreover, analyses were based on self-reports of blood glucose levels. Overall, while the study revealed the positive effects of kombucha on glucose levels in T2D subjects, it was not sufficiently powered to reach definitive conclusions, and thus, large-scale studies are required.