The incidence of obesity has increased significantly in the past decade, along with obesity-related illnesses, such as diabetes and heart disease. According to the U.S. Centers for Disease Control and Prevention, the incidence of diabetes alone may triple by 2050. Medical experts are exhorting overweight individuals to change their eating habits and increase their activity levels, and scientists are earnestly examining specific dietary behaviors, such as green tea consumption, that may contribute to weight loss.
The Search for Functional Foods
The concept of "functional foods" has been discussed in the scientific literature for at least two decades. In 1994, the Institute of Medicine defined a functional food as "any food or food ingredient that may provide a health benefit beyond the traditional nutrients it contains." Examples of such health benefits include antioxidant, anti-inflammatory or anti-tumor properties. Thus, fish oil, red wine and green tea can be considered functional foods owing to their content of omega-3 fatty acids, resveratrol and polyphenols, respectively. America's obesity epidemic has made the search for functional foods that improve weight control particularly relevant.
Thermogenesis
One notion that has captured the minds of scientists -- and the hearts of people who are trying to lose weight -- is a property called "thermogenesis," which refers to a food's innate ability to increase your metabolic rate. Caffeine serves as a prototypical thermogenic agent, due to its ability to increase the activity of your sympathetic nervous system. However, an October, 1995, study in "American Journal of Physiology" shows that the thermogenic effect of caffeine ia actually blunted in obese individuals, which, in addition to its tendency to raise your heart rate and blood pressure, could make caffeine a poor choice for weight loss.
Green Tea and Thermogenesis
The idea that some foods can help people burn fat is an appealing one, but not all scientists agree that thermogenesis can be clinically useful. However, a 1999 trial from "The American Journal of Clinical Nutrition" suggested that green tea possesses thermogenic properties beyond that explained by its caffeine content, and that this functional effect of green tea could be useful for the management of obesity. This study used a green tea extract containing 90 mg of epigallocatechin gallate, or EGCG, which the subjects consumed three times daily. A 2009 review in "American Family Physician" reports that green tea is 20 to 45 percent polyphenols by weight, of which 60 to 80 percent are catechins. Therefore, you could obtain an equivalent dose of EGCG by brewing 750 mg of dry green tea in hot water three times daily.
Considerations
The recommendation that overweight individuals reduce their caloric intake and increase their levels of physical activity is based on a consensus that these are the only known methods to effectively achieve and maintain weight loss. The addition of functional foods or supplements that reputedly increase your metabolic rate may provide additional benefits, but such measures cannot be expected to confer significant weight loss on their own.
References
- U.S. Centers for Disease Control and Prevention: Number of Americans with Diabetes Expected to double or Triple by 2050; October 22, 2010
- Institute of Food Technologists: Functional Foods: Their Role in Disease Prevention and Health Promotion; C.M Hasler; 1998
- "American Journal of Physiology"; Effects of Caffeine on Energy Metabolism, Heart Rate, and Methylxanthine Metabolism in Lean and Obese Women; D. Bracco, et al.; October 1995
- "The American Journal of Clinical Nutrition"; Efficacy of a Green Tea Extract Rich in Catechin Polyphenols and Caffeine in Increasing 24-Hour Energy Expenditure and Fat Oxidation in Humans; A.G. Dulloo, et al.; December 1999
- "American Family Physician"; Green Tea: Potential Health Benefits; C. Schneider, T. Segre; April 2009
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