Grape Seed Extract Supplementation and the Effects on the Biomarkers of Oxidative Stress and Metabolic Profiles in Female Volleyball Players: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

BACKGROUND Only limited data are available for evaluating the effects of the administration of grape seed extract (GSE) on the metabolic status of female volleyball players. OBJECTIVES This study was conducted to determine the effects of GSE administration on the metabolic status of female volleyball players. METHODS This randomized, double-blind, placebo-controlled clinical trial was performed among 40 female volleyball players. The subjects were randomly divided into two groups, with members of the test group (n = 20) taking 300 mg of GSE twice a day for eight weeks and members of the control group (n = 20) taking a placebo pearl for the same period. Fasting blood samples were taken before and after the eight-week intervention period in order to determine the related variables. RESULTS Supplementation with GSE resulted in a significant rise in the plasma glutathione (GSH) level (+265.5 ± 344.2 vs. +2.2 ± 378.2 µmol/L, P = 0.02), as well as a significant decrease in the malondialdehyde (MDA) level (-1.4 ± 2.0 vs. -0.2 ± 1.2 µmol/L, P = 0.01) when compared to the placebo group. In addition, when compared to the group that received the placebo, the subjects who received GSE had significantly decreased serum insulin concentrations (-23.4 ± 23.4 vs. +1.8 ± 25.2 pmol/L, P = 0.002), a decreased homeostasis model of assessment for insulin resistance (HOMA-IR) (-0.7 ± 0.7 vs. +0.2 ± 0.9, P = 0.002), and an increased quantitative insulin sensitivity check index (QUICKI) (+0.01 ± 0.01 vs. -0.01 ± 0.02, P = 0.03). The administration of GSE had no significant effects on creatine phosphokinase (CPK), total antioxidant capacity (TAC), nitric oxide (NO), fasting plasma glucose (FPG), and lipid concentrations when compared with the administration of the placebo. However, after controlling for baseline NO levels, age, and baseline BMI, the changes in the plasma NO concentrations were significantly different between the two groups. CONCLUSIONS In conclusion, taking GSE for eight weeks had beneficial effects on the plasma GSH, MDA levels, and markers of insulin metabolism of female volleyball players.