Black tea kombucha reduces gut bacteria associated with obesity

Key Takeaways:

• Kombucha altered gut microbial composition, particularly in participants living with obesity, by increasing beneficial bacteria and reducing obesity-linked genera.
• Despite these microbial changes, no significant shifts were observed in short-chain fatty acid levels or markers of intestinal permeability.
• Black tea kombucha is rich in phenolic compounds, notably flavonoids, which may contribute to its potential anti-obesity effects.

Introduction

Obesity remains a mounting global health challenge, currently affecting over one billion people worldwide. This complex condition arises from the interplay of genetic, environmental, physiological, and behavioural factors, though the underlying mechanisms are still incompletely understood. Recent research has increasingly focused on the gut microbiota as a potential contributor to obesity and metabolic dysregulation. Dysbiosis—a disruption in the balance and diversity of gut microbes—has been implicated in the development and progression of obesity.

Diet plays a critical role in shaping the gut microbiome. One food item that has garnered significant attention for its potential microbiota-modulating effects is kombucha—a fermented tea produced using a Symbiotic Culture of Bacteria and Yeast (SCOBY). While numerous animal studies have suggested that kombucha, especially when derived from black tea, can beneficially influence the gut microbiome, evidence from human studies remains scarce.

This study, recently published in The Journal of Nutrition, aimed to address this gap by evaluating the effects of daily black tea kombucha consumption over an eight-week period on gut microbiota composition and intestinal health, in adults with and without obesity.

Study Design and Methods

Participant Selection

Out of 193 online respondents, 62 individuals were screened, and 46 met the eligibility criteria. Participants were divided into two groups based on body mass index (BMI):

• Group with normal-weight: Mean BMI of 21.64 kg/m²
• Group with obesity: Mean BMI of 34.47 kg/m²

Inclusion criteria required participants to be between 18 and 45 years old, have a BMI ≥18.5 kg/m², and be free from chronic diseases aside from obesity. Individuals were excluded for a range of reasons including recent antibiotic use, consumption of kombucha in the past month, vitamin supplementation, chronic medication use affecting lipid or glucose metabolism, unstable body weight, or being pregnant, lactating, or smokers.

Intervention and Data Collection

Participants consumed 200 mL of laboratory-prepared black tea kombucha daily for eight weeks. The kombucha was acidic (low pH) with a mildly sweet taste, achieved by controlled fermentation.

Biological samples (blood, stool, and urine) and lifestyle data were collected at baseline and after eight weeks. Participants were asked to maintain their usual diet and physical activity levels, monitored via the Food Frequency Questionnaire (FFQ) and the International Physical Activity Questionnaire (IPAQ).

Laboratory Analyses

The kombucha’s composition was assessed using:

• High-performance and ultra-performance liquid chromatography (HPLC & UPLC-MS)
• Titration and Folin–Ciocalteu colourimetric assays

Microbial profiling was performed via serial dilution techniques, and intestinal permeability was evaluated using lactulose/mannitol urinary ratios and plasma zonulin concentrations. Stool samples were also analysed for short-chain fatty acid (SCFA) content (acetate, butyrate, and propionate).

Key Findings

Kombucha Composition

The black tea kombucha was found to be rich in 145 phenolic compounds, comprising:

• Flavonoids (81%), notably quercetin 3-O-rutinoside
• Phenolic acids (19%)

These compounds are known for their antioxidant and potential anti-obesity properties.

Microbial Changes

The primary outcomes demonstrated a differential response between the normal-weight group and group with obesity:

• Participants with obesity exhibited:
  • Increased abundance of Subdoligranulum, a beneficial butyrate-producing bacterium
  • Reductions in Ruminococcus and Dorea, both genera associated with obesity and inflammation
• These reductions were particularly noteworthy as both Ruminococcus and Dorea were initially present at significantly higher levels in participants with obesity, but were brought down to baseline levels seen in the normal-weight group by the end of the intervention.
• In both groups, kombucha consumption supported the proliferation of:
  • Bacteroidota
  • Akkermanciaceae, both commensal bacterial families associated with improved metabolic health

Fungal Composition

Although kombucha also altered the gut fungal profile, the effects were less conclusive:

• A modest increase in Saccharomyces was observed
• No significant overall change in fungal alpha-diversity
• Participants with obesity had higher fungal diversity at baseline, which may have declined or shifted over the intervention period

Intestinal Permeability and SCFAs

Despite notable microbial shifts, no statistically significant differences were found in:

• Short-chain fatty acid concentrations in stool samples (acetate, butyrate, propionate)
• Intestinal permeability markers, including:
  • Lactulose-to-mannitol urinary ratio
  • Plasma zonulin levels

This suggests that while the microbiome composition changed, functional and physiological biomarkers remained largely unaltered over the eight-week period.

Physical Activity

IPAQ results confirmed that physical activity levels remained consistent throughout the study. This minimises confounding and supports that observed microbiota changes are likely due to the kombucha intervention rather than lifestyle alterations.

Study Limitations

Several limitations are worth noting:

• Lack of a control group: All participants consumed kombucha, meaning that outcomes cannot be compared to a non-intervention group.
• Short duration: Eight weeks may not be sufficient to observe changes in SCFA production or gut barrier function.
• Sample size: While relatively robust for a pilot nutritional intervention, broader generalisations require larger and more diverse cohorts.
• Self-reported data: Dietary intake and activity levels were self-reported and may be subject to bias or inaccuracies.

Conclusions and Future Directions

This study offers promising early evidence that black tea kombucha consumption can beneficially modulate the gut microbiota, especially in people living with obesity. The findings suggest that kombucha may help rebalance the gut microbial ecosystem by increasing beneficial bacteria and reducing those associated with metabolic dysfunction.

However, the absence of changes in SCFA levels and intestinal permeability markers indicates that microbial compositional changes may not immediately translate into functional physiological benefits within the timeframe observed.

Future research should include:

• A randomised control group for comparison
• A longer intervention duration to detect slower-acting effects
• Clinical endpoints such as weight change, lipid profile, and inflammatory markers to better understand the therapeutic potential of kombucha in obesity management

In summary, daily black tea kombucha consumption over eight weeks resulted in favourable changes to the gut microbial landscape, particularly for individuals with obesity. While more comprehensive studies are needed, these findings contribute to the growing evidence base linking fermented foods to gut and metabolic health.

CCH Insight:

This is a very interesting study, but it raises lots more questions about fermented foods, the gut microbiome and obesity than it answers. The fact that just one drink of kombucha per day can positively influence the balance of the gut microflora in relation to obesity is excellent news, but longer-term studies with more participants are needed to see if kombucha can bring about meaningful metabolic changes. And what about other fermented foods, like kefir, yoghurt, sauerkraut and kimchi? Could they also have positive effects, both individually and synergistically? This is a fascinating area of research, which we follow with great interest at CCH.