Effect of Green Tea Extract on Exercise-Induced Oxidative Stress in Obese Men: A Randomized, Double-Blind, Placebo-Controlled, Crossover Study

Background Green tea contains polyphenol catechins that has been shown to be beneficial to health owing to its antioxidant properties. Objectives This study investigated the effects of a 14-day ingestion of green tea extract (GTE) on biomarkers of oxidative stress in obese men undergoing resistance exercise (RE). Methods In a randomized, double-blind, placebo (PL)-controlled, crossover study, ten obese men (age 37.12 ± 5.66 y; height 177 ± 7.7 cm; BMI 32.53 ± 2.52) performed two RE protocols consisting of 3 sets of 6 exercises to exhaustion at 75% of one repetition maximum (1RM) and 2 minute rests between sets, after 14 days of 500 mg of GTE (two capsules per day) or 500 mg PL (two capsules per day) supplementation. Blood samples were collected before (PRE) and immediately after (POST) RE and analyzed for oxidative biomarkers including lipid peroxidation (8-iso PGF_2α) and oxidative DNA damage (8-OHdG). Results Our results showed that a 14-day GTE supplementation did not change lipid peroxidation (P > 0.05); also, no significant alterations for 8-iso PGF_2α between GTE and PL treatments after RE were observed (P > 0.05). However, 14-day GTE supplementation significantly reduced oxidative DNA damage as measured by 8-OHdG after RE compared to PL (P < 0.05). Conclusions The results of this study demonstrated that 14-day supplementation of GTE significantly prevented oxidative DNA damage induced by RE in untrained obese men. However, the potential effects of GTE on oxidative stress after RE in obese people warrants further investigation.