Biological fates of tea polyphenols and their interactions with microbiota in the gastrointestinal tract: implications on health effects.

Tea, made from the leaves of the plant Camellia sinensis, is a popular beverage and the possible beneficial health effects of tea polyphenols (TPP) have been studied extensively. This article discusses the biological fates of TPP and their interactions with the microbiota in the gastrointestinal tract. TPP are absorbed mainly in the small intestine and undergo metabolism in different organs. The unabsorbed TPP entering the colon are degraded by microbiota. Some of the metabolites are also absorbed systemically and excreted in the urine, while those unabsorbed are excreted in the feces. TPP can in turn modify the composition of gut microbiota. In the human and rodent studies reviewed herein, many studies reported a correlation between the observed microbiota changes with lowering blood glucose level or body weight gain. Bacteria species belonging to different genera were identified; however, the effects of TPP at the phyla level were inconsistent among studies. Our recent study identified a few co-abundance groups that were correlated with the blood glucose lowering effect of green tea polyphenols. The "guilds" approach that we used could lead to a more systematic analysis of microbiota changes. The mechanisms by which TPP modulate gut microbiota directly, or through influence on nutrient environment, are discussed. Finally, there are discussions on how the interactions of TPP with microbiota may impact metabolic diseases as well as on some future studies that are needed.