Large yellow tea, made from the tea plant Camellia sinensis, is one of China's most well-known traditional yellow teas, beloved for its unusual burnt flavour.
The Institute of Cancer Research recently reported in a mouse study that yellow tea possessed significant anti-hyperglycaemic properties, more so than green and black teas, therefore confirming that it could be instrumental in the recovery of glucose metabolism disorder.
However, few long-term studies have explored the yellow tea's impact on mice with metabolic syndrome. As such, researchers at China's Anhui Agricultural University conducted a study to comparatively examine the molecular mechanism of dietary supplements of large yellow tea powder and its crude water extracts, as well as their impact on glucose and lipid metabolism, and hepatic steatosis of middle-aged male mice.
Yellow yellow, healthy fellow
The 30 mice (12 control) were put on a regular diet until they were 10 weeks old, after which the control mice were randomly divided into two groups and the rest divided into three groups, each fed a different diet.
They observed that dietary supplements made from large yellow tea and water extract "significantly reduced" food and water intake, and blood glucose level, lowered serum total and LDL cholesterol and triglyceride levels, and increased glucose tolerance in the treated mice when compared with the untreated mice.
Additionally, the dietary supplement of large yellow tea inhibited fatty liver formation and restored the normal hepatic structure of the treated mice.
The researchers wrote that it also led to an obvious reduction in lipid synthesis associated with gene fatty acid synthase, "the sterol regulatory element-binding transcription factor 1 and acetyl-CoA carboxylase α, as well as fatty acid synthase and sterol response element-binding protein 1 expression, while the lipid catabolic genes were not altered in the liver" of the treated mice.
Water or tea?
Epigallocatechin 3-gallate (EGCG) was a major constituent identified in both large yellow tea and its water extract, with a higher concentration in the latter.
Together with higher caffeine and theanine levels, the water extract "saw a remarkable amount of total catechins" when compared with that in large yellow tea.
The mice fed with large yellow tea or its water extract had more normal liver cells than the mice on a standard chow diet.
The researchers also observed that large yellow tea "more profoundly influenced the attenuation of hepatic steatosis" than its water extract did.
They said the study "substantiated that the dietary supplement of large yellow tea has potential as a food additive for ameliorating type 2 diabetes-associated symptoms".
This led them to conclude: "Therefore, we hypothesise that a range of substances not extracted by water in large yellow tea may contribute the principal effects of decreasing blood glucose and alleviating metabolic syndrome in mice. These exact functional components need further investigation."
"Dietary Supplement of Large Yellow Tea Ameliorates Metabolic Syndrome and Attenuates Hepatic Steatosis in db/db Mice"
Authors: Yun Teng, et al.