Effects of Polyphenols in Tea (<em>Camellia Sinensis sp.</em>) on Modulation of Gut Microbiota in Human Trials and Animal Studies

A diet high in polyphenols is associated with a diversified gut microbiome. Tea is the second most consumed beverage in the world, after water. The health benefits of tea might be attributed to the presence of polyphenol compounds such as catechins, theaflavins, tannins, and flavonoids. Although many studies are on tea, little is known of its effects on trillions of gut microbiota. Hence, this review is aimed at systematically studying the effect of tea polyphenols on the stimulation or suppression of gut microbiota in humans and animals. It was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol. Articles were retrieved from PubMed and Scopus databases, and data were extracted from 6 human trials and 15 animal studies. Overall, huge variations were observed in terms of microbiota composition between humans and animals. A more consistent pattern of diversified microbiota was observed in animal studies. Tea alleviated the gut microbiota imbalance caused by high-fat diet-induced obesity, diabetes, and ultraviolet-induced damage. Overall changes in microbiota composition measured by beta diversity analysis showed that tea had shifted the microbiota from the pattern seen in animals that received tea-free intervention. In humans, the prebiotic-like effect was observed towards gut microbiota, but these results appear in lower-quality studies. Beta diversity in human microbiota remains intact despite tea intervention; supplementation with different teas affected different types of bacterial taxa in the gut. These studies suggest that tea polyphenols may have a prebiotic effect in disease-induced animals and in a limited number of human interventions. Further intervention is needed to identify the mechanisms of action underlying the effects of tea on gut microbiota.