Green tea extract does not affect exogenous glucose appearance but reduces insulinemia with glucose ingestion in exercise recovery

We reported that supplementation with green tea extract (GTE) lowered the glycemic response to an oral glucose load following exercise but via an unknown mechanism. Here we examined the effect of supplementation with GTE on plasma glucose kinetics upon ingestion of a glucose beverage during exercise recovery. Eleven healthy, sedentary men (21±2 y; BMI=23±4 kg•m^-2, VO₂peak=38±7 ml•kg^-1•min^-1; mean±SD) ingested GTE (350 mg) or placebo (PLA) thrice daily for 7-d in a double-blind, crossover design. In the fasted state, a primed constant infusion of [U-¹³C₆] glucose was started, and 1-h later, subjects performed a graded-exercise test (25 Watts/3 min) on a cycle ergometer. Immediately post-exercise, subjects ingested a 75g glucose beverage containing 2g of [6,6-²H₂] glucose, and blood samples were collected every 10-min for 3-h of recovery. The rate of carbohydrate oxidation was lower during exercise after GTE vs. PLA (1.26±0.34 vs. 1.48±0.51 g•min^-1, P=0.04). Glucose area under the curve (AUC) was not different between treatments after drink ingestion (GTE=1067±133 vs. PLA=1052±91 mM•180 min, P=0.91). Insulin AUC was lower after GTE vs. PLA (5673±2153 vs. 7039±2588 µIU•180 min, P=0.05), despite similar rates of glucose appearance (GTE=0.42±0.16 vs. PLA=0.43±0.13, g•min^-1, P=0.74) and disappearance (GTE=0.43±0.14 vs. PLA=0.44±0.14, g•min^-1, P=0.57). We conclude that short-term GTE supplementation did not affect glucose kinetics following ingestion of an oral glucose load post-exercise; however, GTE was associated with attenuated insulinemia. These findings suggest GTE lowers the insulin required for a given glucose load during post-exercise recovery, which warrants further mechanistic studies in humans

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