As a phase 0 clinical trial, we will learn how kombucha influences glucose metabolism in humans.

Consumption of kombucha, a fermented tea beverage, has been promoted for a wide range of health benefits. However, a systematic literature review (Kapp & Sumner, 2019) revealed a lack of evidence for human health benefit. Despite the lack of evidence, U.S. retail sales of kombucha and other fermented beverages have increased 37.4% in 2017, and kombucha is the fastest growing product in the functional beverage market.

As a phase 0 clinical trial, we will learn how kombucha influences glucose metabolism in humans. We plan for 20 subjects to take part in this study.

This is a randomized-controlled counter-balanced study design. Subjects will be asked to complete 4 in-person visits over 2 months time (twice per month). At the first visit, subjects will be randomized into one of four groups. At each subsequent visit, subjects will be randomized into one of the remaining groups until they have completed each arm.

Arms (at least 5 subjects in each arm, minimum total=20 subjects)

1. Intervention group 1: commercial kombucha: drink 8oz kombucha
2. Intervention group 2: brewed kombucha: drink 8oz kombucha
3. Control group: drink 8oz tea (the same type as used to brew the kombucha)
4. Control group 2: drink 8oz tap water

Inclusion Criteria:

• Men or women ages 30-65 years old
• English-speaking
• Have transportation to campus
• Overweight (BMI >= 25 kg/m2) or obese (BMI >=30 kg/m2)

Exclusion Criteria:

• Currently use any type of nicotine product

• A diagnosis of any of the following:

  • Diabetes (type 1 or 2)
  • Cancer
  • COPD
  • Chronic alcoholism
  • Peripheral vascular disease
  • Autoimmune disease
  • Chronic kidney disease

• Pregnant or breastfeeding

• Prescribed medication for insulin, glucose-lowering drugs, or steroids, such as prednisone

• Have routinely taken prebiotic or probiotic supplements in the past 3 months

• Have routinely consumed any of the following more than one time per week in the past month: kombucha, kefir, yogurt, kimchi, cottage cheese, raw apple cider vinegar (with the "mother"), sauerkraut, kvass.