Polyphenols in tea increased weight loss and improved energy metabolism by changing the composition of gut bacteria in mice.

Both black and green tea changed the ratio of bacteria in the gut which corresponded with lean body mass. Polyphenols specifically in black tea stimulate the growth of a species of gut bacteria called Pseudobutyrivibrio which increased levels of short-chain fatty acids, a type of bacterial metabolites that have been shown to alter the energy metabolism in the liver.