A study led by nutritional scientist Richard Bruno has found that green tea can help mitigate the impact of nonalcoholic fatty liver disease.
Bruno, an assistant professor of nutritional sciences in the College of Agriculture and Natural Resources, and his research team have found that the daily ingestion of green tea blocks the amount of fat stored in the livers of obese mice that otherwise develop severe fatty liver disease; improves liver function; and reverses declines in antioxidant defenses in the liver.
The researchers found these beneficial effects when genetically obese mice were fed green tea extract for six weeks at doses equivalent to about three to seven cups of liquid green tea per day for humans.
Bruno says that although green tea had previously been found to have benefits for those with heart disease, and lowers cholesterol and triglycerides – risk factors in both heart and fatty liver disease, prior to his study “no one knew whether green tea could protect the liver against fatty liver disease.”
He describes nonalcoholic fatty liver disease as “a silent but potentially deadly disease.”
Two-thirds of Americans are currently overweight or obese, and the incidence of nonalcoholic fatty liver disease – which is very common in people who are obese or diabetic – has risen in parallel with the rates of obesity. “About 40 million people in the U.S. are estimated to have fatty liver disease,” he says, “and unless the obesity epidemic that’s underway is corrected, or we develop new dietary strategies, we should expect the incidence of this disease to increase dramatically.”
Obesity often causes insulin resistance, which results in the alteration of the body’s fat metabolism and leads to excess storage of fat in the liver. The fat-engorged liver increases in size – possibly up to two or three times its normal size – resulting in liver injury or abnormally high liver function tests. Eventually this may lead to liver failure or death.
“Nonalcoholic fatty liver disease is quite serious,” says Bruno, “yet there are currently no pharmacological therapies for it, only recommendations to lose weight and exercise more.”
Bruno and his team are looking at green tea and other dietary antioxidants that may mitigate the processes underlying the disease.
Their research, which has been underway for nearly four years, is currently funded by a two-year, $458,000 grant from the U.S. Department of Agriculture.
The initial study, which was featured on the cover of the Journal of Nutrition in February 2008, showed clearly that green tea reduces fat accumulation in the liver and protects against liver injury, says Bruno. The USDA award is to support research into the mechanisms by which green tea protects against fatty liver disease, and how a reduction in liver fat content improves liver function.
Possible avenues the team is exploring are whether green tea interferes with fat absorption, whether it enhances the rate at which fat is used for energy by the liver, and whether it blocks fat synthesis in the liver.
“There are data to support all three,” says Bruno. “Possibly it affects all of these systems simultaneously.”
He says that although the beneficial impact of green tea is clear from the mouse model, it may not be possible to carry out a human trial, because that would require taking multiple liver biopsies from healthy people as well as those with liver disease, raising ethical issues.
Bruno says green tea is different from other types of tea, even though they come from the same plant. When it is harvested, the leaves are immediately steamed and withered, and this preserves certain compounds known as catechins that are thought to exert beneficial effects on human health.
In the processing of oolong and black tea, however, these compounds are largely destroyed.
Future Research Questions
In future research, he hopes to discover whether the catechins are indeed the part of green tea that is effective, and to analyze each of the four major catechins it contains.
For now, he is focusing on a whole food approach. “My philosophy is that food is a complex matrix,” he says, “and if one compound has an effect, it likely has synergistic effects in the presence of other bioactive food components.”
Bruno, a registered dietitian, says he would recommend green tea as part of a weight loss program, but its effects are limited. “Green tea could be a critical component of a lifestyle change, but it is not a magic bullet,” he says.
“The number one recommendation for losing weight is to exercise, and work with a dietitian to develop a structured program to modify your lifestyle.”
He says he does not recommend taking green tea supplements, since these probably contain only one of the catechins found in green tea.
UConn collaborators include co-investigators Sun Koo, professor and head of nutritional sciences; Joan Smyth, an associate professor of pathobiology; post doctoral fellow Hea Jin Park; doctoral student Min-Yu Chung; and master’s student Dana Dinatale. Ji-Young Lee, a molecular biologist at the University of Nebraska-Lincoln, is also a co-investigator.