Effect of endurance training supplemented with green tea extract on substrate metabolism during exercise in humans

Endurance training and ingestion of green tea extract (GTE), composed mainly of tea catechins (TC), are well known to enhance fat metabolism. However, their synergistic effects remain to be fully elucidated. We tested the hypothesis that endurance training supplemented with GTE would further accelerate whole-body fat utilization during exercise, compared with training alone, in humans. Twelve healthy male subjects [peak oxygen consumption (VO2peak), 50.7 ± 1.3 (SEM) mL/kg/min] were divided into two groups: GTE and placebo (PLA) groups. Subjects in both groups performed a cycle ergometer exercise at 60% of VO2peak for 60 min/day, 3 days/week, and daily ingested 572.8 or 0 mg TC in GTE and PLA groups for 10 weeks, respectively. Before and after training, respiratory gas exchange was measured during 90-min exercise at pre-training ∼55% of VO2peak. After training, the average respiratory exchange ratio during exercise remained unchanged in the PLA group (post-training: 0.834 ± 0.008 vs pre-training: 0.841 ± 0.004), whereas it was lower in the GTE group (post-training: 0.816 ± 0.006 vs pre-training: 0.844 ± 0.005, P<0.05). These results suggest that habitual GTE ingestion, in combination with moderate-intense exercise, was beneficial to increase the proportion of whole-body fat utilization during exercise.