Green tea extract decreases oxidative stress and improves insulin sensitivity in an animal model of insulin resistance, the fructose-fed rat.

BACKGROUND Tea polyphenols, as both insulin potentiating factors and antioxidants, are postulated to act in preventing the metabolic syndrome, which is characterized by insulin resistance, dyslipidemia, and increased oxidative stress. OBJECTIVE AND METHODS Using an animal model of insulin resistance, our objective was to determine the effects of a green tea extract on oxidative stress parameters and insulin sensitivity. Wistar rats, 10 per group, received a high-fructose diet (FD) for 6 weeks, or the same diet (FD) plus 1 or 2 g of green tea solids/kg diet. RESULTS Signs of insulin resistance (hyperglycemia, hypertriglyceridemia, and hyperinsulinemia) developed in rats receiving the FD, but not in those of the control group. In contrast, animals receiving added tea solids exhibited decreases in glycemia, insulinemia, and triglyceridemia, consistent with an insulin-potentiating effect of tea. In parallel, oxidative stress was decreased by tea consumption with lower plasma lipid peroxidation, sulfhydryl (SH) group oxidation, and DNA oxidative damage. In summary, the addition of green tea extracts to the diet, inducing insulin resistance, led to protective effects of green tea against both oxidative stress and insulin resistance. CONCLUSIONS These data suggest that green tea may be beneficial for people with decreased insulin sensitivity and increased oxidative stress, such as those with the metabolic syndrome or type 2 diabetes.