Kombucha, a fermented beverage made from Camellia sinensis tea (black, oolong, or green) with sugar and a symbiotic culture of bacteria and yeast (SCOBY), has gained global attention for its potential health benefits. Factors like the type and amount of sugar substrate, fermentation time, and temperature significantly influence its organic compounds, total phenolics, vitamin content, and alcohol levels. In a previous study, kombucha's impact on glucose tolerance, insulin sensitivity, body composition, and liver function was tested in male prediabetic mice with diet-induced obesity. Daily supplementation (200 µL per mouse) improved glucose tolerance after nine days (equivalent to one year in humans) and reduced liver steatosis, despite no changes in body composition. Although kombucha has been associated with antioxidant, antimicrobial, probiotic, antidiabetic, and anticancer activities, strong scientific evidence in humans remains limited. Further clinical studies are needed to substantiate kombucha's health benefits in humans.
The objectives of this clinical study aim to explore the effects of kombucha on the health of individuals with overweight and class 1 obesity, while also determining whether the kombucha microbiota plays a role in the observed effects. Specifically, by investigating metabolic parameters such as glucose and insulin levels and lipid profile, as well as the composition and diversity of the gut microbiota and liver function, the study will contribute to a deeper understanding of the potential benefits and mechanisms of action of kombucha consumption in humans. The study aims to recruit at least 30 individuals with overweight and class 1 obesity, aged between 18 and 60 years, randomly distributed into 3 arms (each arm should have about 10 participants). The first arm receives a daily amount of 33 cl of kombucha (live drink) for 4 weeks, the second arm receives a daily amount of 33 cl of kombucha (pasteurized drink) for 4 weeks. The control group receives 33 cl of sparkling water for 4 weeks.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
OTHER
Masking
TRIPLE
Enrollment
33
Participants receive a daily amount of 33 cl of live kombucha (non-pasteurized/ non-filtered) for 4 weeks (28 days).
Participants receive a daily amount of 33 cl of kombucha (pasteurized drink) for 4 weeks (28 days).
Participants receive a daily amount of 33 cl of sparkling water for 4 weeks.
Centro de Apoio Tecnológico Agro Alimentar (CATAA)
Castelo Branco, Castelo Branco District, Portugal
RECRUITINGCentro de Apoio Tecnológico Agro Alimentar (CATAA) (facilities temporarily provided by the Affidea clinical analysis center)
Covilha, Portugal
RECRUITINGChange in Gut microbiota composition and diversity (fecal samples)
Analyze the changes in the relative abundance of the microbial species present, including taxonomic identification and diversity analysis, from baseline to the end of intervention, by next-generation sequencing (NGS).
Time frame: 4 weeks
Change in fasting glucose levels
Fasting glucose (mg/dl), from baseline to the end of intervention. Reduction is a better outcome.
Time frame: 4 weeks
Change in fasting insulin levels
Fasting insulin (μUI/mL), from baseline to the end of intervention. Reduction is a better outcome.
Time frame: 4 weeks
Changes in Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) values
HOMA-IR values, from baseline to the end of intervention. Calculated from fasting glucose (mmol/L) X fasting insulin (mU/L) / 22.5). Less than 1.0 means insulin-sensitive, which is optimal. Above 1.9 indicates early insulin resistance. Above 2.9 indicates significant insulin resistance. Reduction is a better outcome.
Time frame: 4 weeks
Changes in Lipid profile
Lipid profile (total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides), in mg/dL, from baseline to the end of intervention.
Time frame: 4 weeks
Stool consistency rating by Bristol Stool Scale
The Bristol Stool Chart is a medical tool used to classify human feces into seven distinct categories. This scale is widely regarded as the gold standard for evaluating stool consistency and intestinal transit time in adults. It ranges from type 1 (separate hard lumps), which indicates the slowest transit time and constipation, to type 7 (watery with no solid pieces), representing the fastest transit time. Daily monitoring questionnaire (to evaluate 1 to 7), from baseline to the end of intervention.
Time frame: 4 weeks
Variation in SIBO diagnosis (positive/negative) measured by methane and hydrogen levels in breath test
Hyrogen and methane lactulose breath test, in ppm, from baseline to end of intervention. Interpretation criteria: SIBO test is positive if there is an early increase (in the first 90 minutes) equal to or greater than 20 ppm of H2 and/or equal to or greater than 10 ppm of CH4, when compared with the lowest value obtained.
Time frame: 4 weeks
Change in liver enzyme levels
Analyze liver enzymes (units: in UI/L) such as alkaline phosphatase, alanine transaminase, aspartate transaminase, gamma-glutamyl transferase, from baseline to end of intervention, to determine potential hepatic effects of Kombucha consumption.
Time frame: 4 weeks
Change in levels of oxidative stress biomarker (ratio 8-iso-PGF2α to prostaglandin F2α (PGF2α))
Measure of oxidative stress biomarker (pg/mL ), from baseline to the end of intervention. Normal human plasma reference values: 40-100 pg/mL.
Time frame: 4 weeks
Change in gastrointestinal symptoms using a Likert scale
Evaluate gastrointestinal symptoms (e.g., bloating, gas) using a 10-point Likert scale, from baseline to the end of intervention. The daily questionnaire goes from zero (0) which means "no pain" to ten (10) which means "worst pain imaginable".
Time frame: 4 weeks
Change in high-sensitive C-reactive protein levels
Levels of h-sensitivity C-reactive protein (hsCRP), a marker of inflammation, in mg/dL, from baseline to the end of intervention. hsCRP levels of less than 0.100, 0.100 to 0.300, and greater than 0.301 mg/dL are associated with lower, moderate, and higher cardiovascular risks, respectively.
Time frame: 4 weeks
Change in Total oxidant capacity
Oxidative stress biomarker, pg/mL, measured from baseline to the end of intervention. Normal values range from 40-100.
Time frame: 4 weeks
Changes in serum albumin and bilirubin levels
Evaluate hepatobiliary function, albumin (g/dL), Bilirubin (mg/dL)
Time frame: 4 weeks
Changes in short chain fatty acids in stool
SCFAs in stool, units µM
Time frame: 4 weeks
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