Consuming the equivalent of five to eight cups of green tea a day was associated with a 5.6 percent decrease in body weight gain, and a 17.8 percent decrease in fat accumulation over eight weeks, according to findings published in Nutrition Research.
On the flip side, the researchers noted a decrease in protein digestion following green tea consumption, report researchers from Poznan University in Poland.
“Although both [1.1 and 2.0 percent green tea aqueous extract] doses improved cardiovascular risk indicators, they, in addition, inhibited protein digestion,” report the researchers.
“For that reason, results obtained in our study indicate some difficulties in reconciling the high effectiveness in prevention of cardiovascular risk factors with low influence on dietary protein digestion,” they added.
Guiding future human trials
Commenting independently, Steven Dentali, PhD, chief science officer for the American Herbal Products Association (AHPA) told NutraIngredients-USA: “The researchers did not find a mechanism of action for these beneficial effects, and it is not known how significant the apparent reduction in protein digestion was,” said Dr Dentali.
“We don’t yet know if this happens in people, but that possibility may help guide the design of future human clinical trials that study green tea for its health benefits,” he added.
The majority of science on tea has looked at green tea, with benefits reported for reducing the risk of Alzheimer's and certain cancers, improving cardiovascular and oral health, as well as aiding in weight management.
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.
The new study adds to the potential weight management effects of green tea, delivered as an green tea aqueous extract.
Researchers led by Joanna Bajerska fed animals a high-fat diet supplemented with 1.1 and 2.0 percent green tea extract for eight weeks. Results showed that the animals had significantly lower measures of atherogenesis of about 14.3 percent, compared to non-supplemented animals.
In additions to the improvements in body weight and decreased fat accumulation for the 2 percent green tea group, the researchers noted that both green tea groups displayed a reduction in digestion of protein of about 17 percent, compared with about 7 percent in the high fat fed animals only.
“It was concluded that green tea extract may have preventive effects on the accumulation of visceral fat but only in higher doses,” wrote Bajerska and her co-workers. “Although both doses improved cardiovascular risk indicators, they, in addition, significantly inhibited protein digestion.”
Source: Nutrition Research
Volume 31, Issue 2, Pages 157-164
“Green tea aqueous extract reduces visceral fat and decreases protein availability in rats fed with a high-fat diet”
Authors: J. Bajerska, M. Wozniewicz, J. Jeszka, S. Drzymala-Czyz, J. Walkowiak