A class of antioxidants in green tea called polyphenols is responsible for the potential benefits -- ranging from cancer prevention to cholesterol control -- of this health-promoting drink quaffed by humans for thousands of years. According to the University of Maryland Medical Center, green tea may also boost metabolism and help burn fat. Researchers at Penn State University have found the combination of green tea and regular exercise boosts fat-burning in mice, but it doesn't seem to matter when the tea is consumed. Drinking any type of caffeine before a workout, however, may give you the energy to go longer, thus increasing the burn.
Metabolism-Boosting Effects of Green Tea
Whether you work out or not, drinking green tea may provide a slight boost to your metabolism, the processes by which your body turns food into energy. A slower metabolism can cause you to put on excess weight. Both the catechins and the caffeine in green tea have metabolism-boosting effects -- caffeine promotes fat-burning by increasing thermogenesis, or heat production, and catechins seem to boost fat oxidation. The two may work in tandem to boost metabolism, according to a review published in "American Journal of Physiology" in July 2006. A study published in "The American Journal of Clinical Nutrition" in December 1999 found that consumption of a green tea extract resulted in a 4 percent increase in 24-hour calorie burn compared to a placebo.
Caffeine and Exercise Performance
Drinking green tea before a workout may help you increase your fat-burning results simply due to the caffeine in the drink. Caffeine gives you a boost of energy, which may help you work out for a longer period of time. Many endurance athletes supplement with caffeine for precisely this reason. A review published in "Journal of Strength and Conditioning Research" in January 2009 analyzed the results of 21 studies on caffeine's effects on sport-specific endurance and concluded that caffeine can be effective before exercise in moderate quantities for improving endurance.
Enhanced Endurance and Fat-Burning Effects of Green Tea
Green tea catechins may have a larger role in the fat-burning effects of green tea than its caffeine content. A study published in "American Journal of Physiology" in March 2005 tested the effects of green tea extract on endurance and fat oxidation in mice. They found that supplementation with green tea extract over 10 weeks led to an increase in endurance of 8 to 24 percent. They also found that green tea extract supplementation promoted increased use of fat as an energy source. Researchers told the American Physiological Society that the amount of green tea extract used in the study was equivalent to about 4 cups of green tea daily.
It may not matter when you drink green tea. The combination of green tea and regular exercise may still lead to enhanced fat-burning and significant weight loss -- more than exercise alone -- say Penn State researchers. Furthermore, their study, which was published in "Molecular Nutrition Food Research" in December 2013, used decaffeinated green tea, showing that even if you're sensitive to caffeine, you can still reap the benefits without getting the jitters.