Drinking green tea after a meal might boost satiety levels, but has very little effect on blood glucose levels or glycemic index, according to a new study.
The research, published in the Nutrition Journal, suggests that the antioxidant-rich beverage could boost feelings of fullness, but found no evidence to support previous suggestions that it may moderate insulin sensitivity or glucose levels.
The researchers, led by Dr Julija Josic from Lund University, Sweden, said the overall sensation of satiety was boosted more after a meal accompanied by green tea than after a reference meal accompanied by water. They said their conclusions that green tea significantly boosted satiety were supported by the fact that “not only was satiety increased, but also the feeling of fullness and the feeling of having had enough to consume.”
The compounds thought to contribute to the health-promoting effects ascribed to green tea are polyphenolic compounds called catechins, which have been the focus of many previous studies on green tea, due to their anti-oxidative properties and their potential role in preventing cancer and cardiovascular disease.
But some research has also suggested a possible link between green tea consumption and diabetes risk, reporting that tea drinking could bring modest benefits for glucose homeostasis and insulin sensitivity.
There are four major catechins in green tea: epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC) and epigallocatechin gallate (EGCG), of which EGCG is the most abundant.
The authors said that intervention studies with green tea extract in healthy rodents and humans have demonstrated increased insulin sensitivity after an oral glucose tolerance test with EGCG was found to have most insulin-enhancing activity in animal in vitro studies.
However,H several studies have observed that neither green tea extracts nor EGCG have any effect on fasting glucose, insulin sensitivity or glucose levels.
“To our best knowledge, this is the first study to examine the effect of green tea on both the glucose metabolism and satiety, after the ingestion of a regular meal,” said the researchers.
“The primary objective of this study was to determine whether ingestion of a regular meal and green tea lower postprandial [post-meal] plasma glucose levels, glycemic index, and insulin levels. The secondary objective, was to establish whether consumption of a regular meal including green tea increase the satiety,” they added.
No significant differences in serum insulin levels or insulin were reported between the green tea meal and a reference meal during a 120 min post-meal observation period.
Josic and colleagues also observed no difference in glucose levels, with 120 min glucose value found to be higher following the green tea meal, and there was no significant difference found in mean glycemic index between the green tea and reference meal.
After the reference meal, the subjects reported finding it more pleasant to eat another mouthful of the same food than after the green tea meal, again confirming the increased feeling of satiety.
Josic and co workers said that differences in taste perception between the green tea and control water drink may have been responsible for the satiety-promoting effects, and so contributed to a stronger satiety sensation after the green tea meal than after the reference meal. They noted that measurements of taste perception during the meals would have provided additional information about this potential confounder.
Source: Nutrition Journal
Volume 9, Issue 63, doi: 10.1186/1475-2891-9-63
“Does green tea affect postprandial glucose, insulin and satiety in healthy subjects: a randomized controlled trial”
Authors: J. Josic, A.T. Olsson, J. Wickeberg, S. Lindstedt, J. Hlebowicz