Supplementing the diet of lab animals fed a high-fat diet with black tea extracts suppressed body weight gain and body fat levels, with the benefits linked to reduced fat absorption, according to findings published in Nutrition.
Interest in tea and its constituents has bloomed in recent years, with the greatest focus on the leaf’s polyphenol content. 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 (EGC), epicatechin gallate (ECG), and epicatechin (EC).
Most of the studies have focussed on green tea and its constituents, most notably EGCG. To date green tea has been linked to a reduced risk of Alzheimer's and certain cancers, improved cardiovascular and oral health, as well as benefits in weight management.
“Although black tea extract contains only small amounts of these components, significant physiologic effects of administering black tea extracts were observed,” wrote researchers from the Functional Food Business Project at Kirin Holdings Company.
“It has been reported that the primary polyphenols in black tea are theaflavins and thearubigins. However, it has not yet been clarified whether thearubigins also have a preventive effect on obesity. Our results are consistent with the possibility that black tea-derived polyphenols are responsible for the observed physiologic effects of the black tea extracts,” they added.
The Japanese scientists fed male rats a fat emulsion containing the black tea extract at a level of 500 or 1,000 mg per kg of body weight. Fat levels in the blood were subsequently evaluated and showed that the black tea extract “suppressed increases in rat plasma triglyceride levels in a dose-dependent manner”, said the researchers.
In a separate study with female mice, the researcher supplemented their high-fat diets with either 1 or 5 per cent of the tea extract for eight weeks.
“Administration of the 5 per cent black tea extract suppressed increases in body weight, adipose tissue mass, and liver lipid content (reduced to 56.9 and 81.7 per cent of control mice, respectively) in mice fed a high-fat diet,” they stated.
While more research is needed, the researchers concluded that the polymerized polyphenol fraction of the black tea was responsible for the apparent weight management benefits.
Published online ahead of print, doi: 10.1016/j.nut.2010.01.019
“Prevention of diet-induced obesity by dietary black tea polyphenols extract in vitro and in vivo”
Authors: S. Uchiyama, Y. Taniguchi, A. Saka, A. Yoshida, H. Yajima