For decades, new age health gurus and tea aficionados have expounded the benefits of drinking the brewed elixir. In recent years, scientific evidence has backed some of the health claims—especially in relation to modest weight loss—although specific molecular mechanisms for how tea exerted its influence on cells of the body has remained elusive. Now, investigators at UCLA have demonstrated that tea, and in particular black tea, may promote weight loss and other health benefits by changing bacteria within the gut. Findings from the new study—published recently in the European Journal of Nutrition, in an article entitled “Decaffeinated Green and Black Tea Polyphenols Decrease Weight Gain and Alter Microbiome Populations and Function in Diet-Induced Obese Mice”—show that in mice black tea alters energy metabolism in the liver by changing gut metabolites.

“It was known that green tea polyphenols (GTPs) are more effective and offer more health benefits than black tea polyphenols (BTPs) since green tea chemicals are absorbed into the blood and tissue,” explained lead study investigator Susanne Henning, Ph.D., an adjunct professor at the UCLA Center for Human Nutrition, which is part of the David Geffen School of Medicine at UCLA. “Our new findings suggest that black tea, through a specific mechanism through the gut microbiome, may also contribute to good health and weight loss in humans.”

Interestingly, the study found that both 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.

“The results suggest that both green and black teas are prebiotics, substances that induce the growth of good microorganisms that contribute to a person’s well-being,” Dr. Henning noted.

Previous studies have indicated that chemicals in green tea called polyphenols are absorbed and alter the energy metabolism in the liver. The new findings show that BTPs, which are too large to be absorbed in the small intestine, stimulate the growth of gut bacterium and the formation of short-chain fatty acids, a type of bacterial metabolites that have been shown to alter the energy metabolism in the liver.

In the current study, four groups of mice received different diets—two of which were supplemented with green tea or black tea extracts:

· Low-fat, high-sugar;

· High-fat, high-sugar;

· High-fat, high-sugar and green tea extract;

· High-fat, high-sugar and black tea extract.

Amazingly, the research team found that after four weeks the weights of the mice that were given green or black tea extracts dropped to the same levels as those of the mice that received the low-fat diet throughout the study. Moreover, the investigators collected samples from the mice’s large intestines (to measure bacteria content) and liver tissues (to measure fat deposits). In the mice that consumed either type of tea extract, there was less of the type of bacteria associated with obesity and more of the bacteria associated with lean body mass.

However, only the mice that consumed black tea extract had an increase in a type of bacteria called Pseudobutyrivibrio, which could help explain the difference between how black tea and green tea change energy metabolism.

“BTP increased the relative proportion of Pseudobutyrivibrio and intestinal formation of short-chain fatty acids (SCFA) analyzed by gas chromatography,” the authors wrote. “Cecum propionic acid content was significantly correlated with the relative proportion of Pseudobutyrivibrio. GTP and BTP induced a significant increase in hepatic 5′adenosylmonophosphate-activated protein kinase (AMPK) phosphorylation by 70 and 289%, respectively (P < 0.05) determined by Western blot.”

The researchers noted that these new findings suggest 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.

“For black tea lovers, there may be a new reason to keep drinking it,” concluded senior study investigator Zhaoping Li, M.D., director of the UCLA Center for Human Nutrition and chief of the UCLA Division of Clinical Nutrition.