Effects of Timing of Acute and Consecutive Catechin Ingestion on Postprandial Glucose Metabolism in Mice and Humans.

We examined the effects of the timing of acute and consecutive epigallocatechin gallate (EGCG) and catechin-rich green tea ingestion on postprandial glucose in mice and human adults. In mouse experiments, we compared the effects of EGCG administration early (morning) and late (evening) in the active period on postprandial glucose. In human experiments, participants were randomly assigned to the morning-placebo (MP, n = 10), morning-green tea (MGT, n = 10), evening-placebo (EP, n = 9), and evening-green tea (EGT, n = 9) groups, and consumed either catechin-rich green tea or a placebo beverage for 1 week. At baseline and after 1 week, participants consumed their designated beverages with breakfast (MP and MGT) or supper (EP and EGT). Venous blood samples were collected in the fasted state and 30, 60, 120, and 180 min after each meal. Consecutive administration of EGCG in the evening, but not in the morning, reduced postprandial glucose at 30 (p = 0.006) and 60 (p = 0.037) min in the evening trials in mice. In humans, ingestion of catechin-rich green tea in the evening decreased postprandial glucose (three-factor analysis of variance, p < 0.05). Thus, catechin intake in the evening more effectively suppressed elevation of postprandial glucose.

Effects of timing of acute catechin-rich green tea ingestion on postprandial glucose metabolism in healthy men.

Green tea polyphenols, particularly catechins, decrease fasting and postprandial glucose. However, no studies have compared the timing of green tea ingestion on glucose metabolism and changes in catechin concentrations. Here, we examined the effects of timing of acute catechin-rich green tea ingestion on postprandial glucose metabolism in young men. Seventeen healthy young men completed four trials involving blood collection in a fasting state and at 30, 60, 120, and 180 min after meal consumption in a random order: 1) morning placebo trial (09:00 h; MP trial), 2) evening placebo trial (17:00 h; EP trial), 3) morning catechin-rich green tea trial (09:00 h; MGT trial), and 4) evening catechin-rich green tea trial (17:00 h; EGT trial). The concentrations of glucose at 120 min (P=.031) and 180 min (P=.013) after meal intake were significantly higher in the MGT trials than in the MP trials. Additionally, the concentration of glucose was significantly lower in EGT trials than in the EP trials at 60 min (P=.014). Moreover, the concentrations of glucose-dependent insulinotropic polypeptide were significantly lower in the green tea trials than in the placebo trials at 30 min (morning: P=.010, evening: P=.006) and 60 min (morning: P=.001, evening: P=.006) after meal intake in both the morning and evening trials. Our study demonstrated that acute ingestion of catechin-rich green tea in the evening reduced postprandial plasma glucose concentrations.