According to the article "Green Tea Supplementation Affects Body Weight, Lipids, and Lipid Peroxidation in Obese Subjects with Metabolic Syndrome", Green tea increases metabolism and fat loss:
Green tea beverage consumption (4 cups/d) or extract supplementation (2 capsules/d) for 8 weeks significantly decreased body weight and BMI. Green tea beverage further lowered lipid peroxidation versus age- and gender-matched controls, suggesting the role of green tea flavonoids in improving features of metabolic syndrome in obese patients.
Is there any information available concerning the mechanism of that metabolic increase?