You may have heard the hype around green tea and weight loss. With no end to the American obesity epidemic in sight, consumers are clamoring for any available aid that will simplify weight reduction. But questions remain as to whether any increase in metabolism and subsequent weight loss associated with green tea is due to the tea itself or the caffeine it contains.
Basics of Green Tea
Black, oolong and green tea all originate from the same plant, Camellia sinensis, but they differ in the way the tea leaves are processed, according to the University of Maryland Medical Center. Black tea is fully fermented, meaning that it undergoes a process that involves rolling and breaking down the leaves so that they are oxidized.
Fermentation and Active Ingredients
Fermentation destroys some of the chemical components of the tea, such as the antioxidants that are credited with giving green tea many of its healthful qualities. Fermentation also increases the caffeine content of tea. Oolong is only partially fermented. Green tea is not fermented, which means that it maintains high levels of antioxidants called catechins and low levels of caffeine when compared to black or oolong tea.
Caffeine, Catechins and Weight Loss
Numerous randomized controlled trials have been conducted to determine whether green tea affects weight loss, according to "The American Journal of Clinical Nutrition." These studies have produced conflicting results, but they have addressed the question of whether any connection between green tea and increased metabolism is merely an effect of the caffeine in green tea. It appears that the catechins in green tea do not affect weight loss by themselves, but only in conjunction with caffeine. Caffeine-free green tea extract had no effect on measurements of human weight or body proportion and thus may not affect metabolism on its own.
It's Not Just the Caffeine
These results may lead you to conclude that it is just the caffeine in green tea that aids in weight loss, but researchers would disagree. In a study that compared subjects who drank a green tea catechin and caffeine beverage with those who consumed an equal amount of caffeine but no catechins, the catechin-consuming group tended to have greater reductions in weight and abdominal fat and lower serum triglyceride levels. The study, published in "The Journal of Nutrition" in 2009, indicates that green tea catechins are believed to promote weight loss by increasing metabolism, but it appears that their effects are only seen when combined with those of caffeine.
References
- University of Maryland Medical Center; Green Tea; David Zieve, MD, MHA, and David R. Eltz; September 2010
- "The American Journal of Clinical Nutrition"; Effect of Green Tea Catechins With or Without Caffeine on Anthropometric Measures: A Systematic Review and Meta-Analysis; Olivia J. Phung, et al.; January 2010
- "The Journal of Nutrition"; Green Tea Catechin Consumption Enhances Exercise-Induced Abdominal Fat Loss in Overweight and Obese Adults; Kevin C. Maki, et al.; February 2009
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