Ohio State University (OSU) researchers fed mice a diet of two percent green tea extract and found that they fared far better than those that ate a diet without it—prompting an upcoming study of green tea’s potential benefits in people at high risk of diabetes and heart disease. Findings from the new study were published recently in the Journal of Nutritional Biochemistry, in a paper titled, “Green tea extract prevents obesity in male mice by alleviating gut dysbiosis in association with improved intestinal barrier function that limits endotoxin translocation and adipose inflammation.” The benefits seen in the new study, appear to stem from improved gut health, including more beneficial microbes in the intestines of the mice.
“This study provides evidence that green tea encourages the growth of good gut bacteria, and that leads to a series of benefits that significantly lower the risk of obesity,” explained senior study investigator Richard Bruno, PhD, professor of human nutrition at OSU.
Negative changes in the gut microbiome have been previously linked to obesity, and green tea has been shown to promote healthy bacteria. The OSU team wanted to explore whether there was an argument for green tea preventing obesity, inflammation, and other factors connected to poor metabolic health, said Bruno, who is also a member of the Ohio Agricultural Research and Development Center.
“The results of studies looking at obesity management so far have been a real mixed bag,” Bruno remarked. “Some seem to support green tea for weight loss, but a lot of other research has shown no effect, likely due to the complexity of the diet relative to a number of lifestyle factors. Our goal is to figure out how it prevents weight gain. This will lead to better health recommendations.”
The research team suspected that green tea might prevent obesity and protect against inflammation in the gut based on previous studies, so they devised an experiment that examined green tea’s effects in male mice fed a normal diet and a high-fat diet designed to cause obesity. (Female mice are resistant to diet-induced obesity and insulin resistance, a precursor to diabetes, so they weren’t included.)
“We hypothesized that catechin-rich green tea extract (GTE) would protect against obesity-associated TLR4/NFκB inflammation by alleviating gut dysbiosis and limiting endotoxin translocation,” the authors wrote. “Male C57BL/6J mice were fed a low-fat (LF) or high-fat (HF) diet containing 0% or 2% GTE for 8 weeks. At week 7, fluorescein isothiocyanate (FITC)-dextran was administered by oral gavage before assessing its serum concentrations as a gut permeability marker.”
The investigators found that mice fed a high-fat diet supplemented with green tea gained about 20% less weight and had lower insulin resistance than mice fed an otherwise identical diet without tea. Moreover, those mice also had less inflammation within fat tissue and the intestine. Furthermore, the green tea appeared to protect against the movement of endotoxin, the toxic bacterial component, out of their guts and into the bloodstream.
Additionally, the OSU team found that the green tea appeared to contribute to a healthier microbial community in the guts of the mice fed a high-fat diet. Mice fed the normal, or low-fat, diet supplemented with green tea also had benefits including reduced weight gain and lower endotoxin levels and markers gut permeability, but these were relatively modest compared with the effects were seen in mice fed the high-fat diet.
Green tea consumption in the experiment would be equivalent to about 10 cups of green tea throughout the day for a person. “It might seem like a lot of tea, but it’s not highly unusual in certain parts of the world,” Bruno said.
The researchers are currently working on a human study that will explore the effects of green tea on gut permeability in people with metabolic syndrome—a condition that predisposes people to type 2 diabetes and heart disease.
For now, it’s too soon to extrapolate the findings in animals to people. He also cautioned that—should the benefits prove true in humans—green tea supplements would not be an obvious substitute for drinking the beverage over the course of a day, because of how the body metabolizes the catechins in the tea.
“Consuming a little throughout the course of a day with food—like the mice did in this study—might be better,” Bruno noted.
The investigators are hopeful that future research will determine whether drinking green tea might be a good strategy for those looking to reduce their chances of becoming obese.
“Two-thirds of American adults are overweight or obese, and we know that just telling people to eat less and exercise more isn’t working. It’s important to establish complementary health-promoting approaches that can prevent obesity and related problems,” Bruno concluded.
