A study in mice may reveal why taking green tea extract may allow you to exercise longer and mobilize (burn) fat stores. In a 10-week study, swimming times to exhaustion for mice fed green tea extract were prolonged by 8 percent to 24 percent, depending on dosage. They also had lower respiratory quotients and higher rates of fat oxidation. Plasma lactate concentrations in the green tea extract-fed mice were significantly lower after exercise, while plasma free fatty acid concentrations were elevated, suggesting they increased their burning of fat as an energy source. The researchers concluded that green tea extract stimulates fat burning resulting in improved endurance capacity.

Reference: Murase T, Haramizu S, Shimotoyodomi A, et a. Green tea extract improves endurance capacity and increases muscle lipid oxidation in mice. Am J Physiol Regul Integr Comp Physiol. 2005 Mar;288(3):R708-15. Epub 2004 Nov 24.