The authors of the above systematic literature search reviewed a total of 262 articles but found no research examining the effects of kombucha on human health. A search on Pubmed conducted in May 2020 also revealed no randomised controlled trial data on results in human subjects.
What does this mean? It means that the health benefits regarding kombucha are either theoretical or based on laboratory and animal studies.
Examination of non-human research (i.e. lab-based and animal studies) suggests that the benefits of Kombucha are derived from the tea and fermentation process that results in production of polyphenols, phenols, B-complex vitamins, glucuronic acid and acetic acid. Some of the health benefits reported include effects on liver and gastrointestinal function, immune function, detoxification as well as antioxidant and antimicrobial effects. However, these effects are yet to be proven in human subjects.
Kapp JM, Sumner W. Kombucha: a systematic review of the empirical evidence of human health benefit. Ann Epidemiol. 2019 Feb;30:66-70. doi: 10.1016/j.annepidem.2018.11.001. Epub 2018 Nov 10. PMID: 30527803.