The effects were observed at relatively low doses of EGCG, report researchers in Molecular Nutrition & Food Research, making a “compelling case for studies in human subjects”.
The effects of the green tea extract may be linked to its ability to inhibit the action of the enzyme responsible for starch digestion – alpha-amylase – said researchers from the Department of Food Science at The Pennsylvania State University.
By inhibiting starch digestion, green tea extracts may reduce the risk of chronic diseases such as type-2 diabetes, often linked to the consumption of diets containing foods with a high glycemic index/load, they said.
The study adds to the list of potential health benefits of green tea and the compounds it contains.
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, and helping with weight management.
Green tea contains between 30 and 40% 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).
The Penn State scientists examined the effect of giving EGCG (93% pure, Taiyo Green Power, China) at a dose of 100 mg per kg along with common corn starch, maltose, sucrose, or glucose to fasted mice.
Results showed that the green tea extract was associated with a significant 50% decrease in peak blood sugar levels when provided with the corn starch, compared with control animals. On the other hand, no effects were observed when EGCG was administered along with maltose or glucose.
This observation suggested that “EGCG may modulate amylase-mediated starch digestion”, they said.
Further lab tests revealed that EGCG could indeed inhibit amylase activity.
“These results suggest that co-administration of green tea or EGCG may represent an effective means to reduce the glycemic effect of high starch foods, and indicates that further studies in human subjects are warranted,” they concluded.
Source: Molecular Nutrition & Food Research
Published online ahead of print, doi: 10.1002/mnfr.201200206
“Inhibition of starch digestion by the green tea polyphenol, (−)-epigallocatechin-3-gallate”
Authors: S.C. Forester, Y. Gu, J.D. Lambert