No effects of three-week consumption of a green tea extract on time trial performance in endurance-trained men

The purpose of this study was to examine the effects of three-week consumption of green tea extract (GTE) supplementation on time trial performance and metabolism during cycling in endurance athletes. Nine endurance-trained men participated in this double-blind and placebo-controlled cross-over study. At the end of the supplementation period with GTE (159 mg/day total catechins) or placebo, respectively, subjects cycled at 50 % of the individual maximal power output for 2 hours, followed by a 30-minute time trial. Respiratory gas exchange, fatty acids, 3-beta-hydroxybutyrate, lactate, glucose, interleukin-6, thiobarbituric acid reactive substances, creatine kinase, and C-reactive protein (CRP) were measured 1 hour before, during, and 1 hour after the exercise test. Blood lipids were measured at rest before cycling. There was no significant effect on performance, energy metabolism, or any other measured parameter, except for CRP, which was significantly reduced (p = 0.045) after GTE supplementation compared to placebo. GTE supplementation did not affect time trial performance and energy metabolism in endurance-trained men in the non-fasting state. Further studies with athletes, particularly in the fed state, but with higher GTE doses, are needed to address the question whether green tea may influence energy metabolism and performance in athletes.