"After comparing blood sugar averages between drinking kombucha or a placebo, they learned that just 4 weeks of drinking kombucha lowered fasting blood sugar levels before meals from 164 to 116 milligrams per deciliters (mg/dL) on average.
For comparison, the American Diabetes Association says normal fasting glucose before meals is 80–130 mg/dL."
https://www.medicalnewstoday.com/articles/kombucha-may-help-control-blood-sugar-in-type-2-diabetes