An October 2017 study by UCLA concluded that, “black and green tea changed the ratio of intestinal bacteria in the animals: The percentage of bacteria associated with obesity decreased, while bacteria associated with lean body mass increased.”
Dr. Zhaoping Li, chief of the UCLA Division of Clinical Nutrition said that, “the findings suggest that the health benefits of both green tea and black tea go beyond their antioxidant benefits, and that both teas have a strong impact on the gut microbiome.” Source: EurekAlert!, the online, global news service operated by AAAS, the science society.
For the Tibb (Islamic Medicine) food qualities of black and green tea see: food qualities