Nonalcoholic fatty liver disease (NAFLD) is a significant global health problem that is expected to worsen. Because of the high prevalence of risk factors such as obesity and type 2 diabetes, fatty liver disease is anticipated to afflict more than 100 million people by 2030, according to Joshua Lambert, associate professor of food science. While weight loss can cut down on the fat content in one’s liver, there are currently no medications approved for NAFLD.
In the study, mice were fed a high-fat diet for 16 weeks. They consumed green tea extract and exercised regularly by running on a wheel, and were found to have just one quarter of the lipid deposits in their livers compared to those seen in the livers of a control group of mice. Mice that were treated with green tea extract alone or exercise alone had roughly half as much fat in their livers as the control group.
In addition to analyzing the liver tissues of mice in the study, which was published recently in Journal of Nutritional Biochemistry, researchers also measured the protein and fat content in their feces. They found that the mice that consumed green tea extract and exercised had higher fecal lipid and protein levels.
“By examining the livers of these mice after the study concluded and by screening their feces during the research, we saw that the mice that consumed green tea extract and exercised actually were processing nutrients differently — their bodies were handling food differently,” Lambert said.
“We think the polyphenols in green tea interact with digestive enzymes secreted in the small intestine and partially inhibit the breakdown of carbohydrates, fat and protein in food,” Lambert continued. “So, if a mouse doesn't digest the fat in its diet, that fat and the calories associated with it pass through the mouse's digestive system, and a certain amount of it ends up coming out in its feces.”
It may be significant, Lambert said, that mice treated with both green tea extract and exercise had higher expression of genes related to the formation of new mitochondria. That gene expression is important, he said, because it provides markers that will help researchers understand the mechanism by which green tea polyphenols and exercise might work together to mitigate fatty liver deposits.
Lambert suggested that people should engage in more physical activity, and that replacing high-calorie beverages with decaffeinated, zero-calorie green tea is a smart move. Combining the two might have health benefits for people, he added, but that claim has not yet been backed any clinical data.
More research is needed to see if there is a synergy created by green tea extract and exercise working together to reduce fat deposited in the liver, or if the effects are simply additive, Lambert suggested.
His research group in the College of Agricultural Sciences has spent 12 years studying the health benefits of polyphenols (often called antioxidants) including green tea, cocoa, avocados and other sources.
In previous related research, Lambert and his colleagues demonstrated that green tea extract and exercise together sharply reduced body mass and improved cardiovascular health of high-fat-fed mice.
Because no human trials assessing the health benefits and risks of green tea combined with exercise have been conducted, he urges caution for people who decide to experiment with the health strategy on their own.
Also involved in the research were Weslie Khoo, Benjamin Chrisfield and Sudathip Sae-tan, graduate students in the Department of Food Science.
The National Institutes of Health and the U.S. Department of Agriculture supported this work.