If the results can be translated to humans, green tea and its extracts could become a useful preventative in the development of fatty liver, a condition that is usually symptomless but said to increase the risk for liver inflammation, and ultimately results in liver failure.
Fatty liver is reportedly on the rise in the US, with between one quarter and one half of Americans, and the prevalence if nonalcoholic fatty liver disease (NAFLD) has increased in line with the ongoing obesity epidemic, state the researchers in the Journal of Nutrition .
Richard Bruno and colleagues from the University of Connecticut used genetically-obese mice (ob/ob) and, using lean mice as a comparison, fed them a diet containing zero, one, or two per cent green tea extract (GTE) for six weeks.
At the end of the study, the researchers report that the obese mice fed the GTE-supplemented diets had 23 to 25 per cent less body than the obese mice fed the non-supplemented diet.
Moreover, the lean mice fed the GTE-supplemented diets had 11 to 20 per cent less body than their lean counterpart on the non-supplemented diet.
Measurements of the blood enzymes alanine aminotransferase and aspartate aminotransferase, used as markers of liver damage, showed that GTE-supplementation was associated with 30 to 41 per cent and 22 to 33 per cent lower activities, respectively.
It is also noted that no significant differences were observed in food intake between lean and obese animals in any group, a result that suggested the extract worked by decreasing intestinal fat absorption or altering liver fat metabolism.
"Nearly 40 million Americans are afflicted with this silent and tragic disease.
Weight loss is the primary recommendation for those with fatty liver disease.
Since this is difficult for most people, we hope that our continued studies on green tea will lead to the understanding of its protective properties and to what extent green tea protects humans from this disease," said Bruno.
"Further study is underway to define the events by which GTE protects against obesity-triggered NAFLD," concluded the researchers.
Green tea is a rich source of catechins, compounds suggested to play a beneficial role in reducing the risk of various diseases, including Alzheimer's, certain cancers, cardiovascular and oral health, with some, namely epigallocatechin gallate (EGCG), now emerging as particularly powerful.
Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent.
Oolong tea is semi-fermented tea and is somewhere between green and black tea.
The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin.
Previous in vitro and in vivo studies reported that high-purity EGCG could help with weight loss, and three mechanisms were proposed: EGCG could increase energy metabolism and fatty acid oxidation; inhibit fat cell development (apidogenesis); and/or reduce lipid absorption and increase fat excretion.
Source: Journal of Nutrition February 2008, Volume 138, Pages 323-331 "Green tea extract protects leptin-deficient, spontaneously obese mice from hepatic steatosis and injury" Authors: R.S. Bruno, C.E. Dugan, J.A. Smyth, D.A. DiNatale, S.I. Koo