According to the National Institute of Diabetes and Digestive and Kidney Diseases, over two-thirds of U.S. adults are overweight or obese. For these individuals, associated health risks are significantly reduced with a modest weight loss of 5 to 10 percent of body weight. Green tea is just one of the many tools being considered to help with weight management.
While extensive research has been performed on green tea and weight loss, results are not conclusive. However, evidence does suggest green tea may boost metabolism and burn fat. Substances known as catechins are thought to be responsible for these effects.
Catechins
Catechins belong to a class of plant chemicals known as polyphenols, which are potent antioxidants. Various catechins are found in green tea, but the most active is epigallocatechin-3-gallate (EGCG). Catechins are thought to be responsible for thermogenesis, which is the production of heat within the body. This heat production is related to energy expenditure or calorie "burn" by using fat stores to stoke the fire. EGCG is thought to inhibit certain enzymes, which are responsible for degrading norepinephrine in the brain. By inhibiting this enzyme, norephinephrine action is prolonged, leading to extended action of thermogenesis.
Regular or Decaf?
In 2010, the "American Journal of Clinical Nutrition" published an analysis of several green tea studies in which weight loss and caffeine content were examined. Phung et al. found green tea was more effective for decreasing body mass index (BMI), body weight, and weight circumference when caffeine was present. Decaffeinated green tea does not appear to significantly alter weight or associated measures. In another 2010 study, published in "Physiology & Behavior," Westerterp-Plantega found caffeine in green tea contributes to the stimulation of fat oxidation and thermogenesis, thereby effecting body weight and energy expenditure.
Available Forms
Green tea is primarily sold as dried leaf tea or as an extract in capsule and liquid forms. Purchasing standardized extracts of green tea is advised.
Dosing
The University of Maryland Medical Center recommends two to three cups of green tea per day providing an approximate amount of 240 to 320mg total polyphenols depending on the type and brand of the tea as well as the size of the cup used. For standardized green tea extract, 100 to 750mg per day is suggested, however, it should be noted that there has been more research on beverages than capsules. Green tea is not recommended for infants or children under the age of 18.
Precautions
In many green tea studies, reports of side effects are minimal or are omitted completely; however, certain people should use caution. Caffeine may cause insomnia in adults, children and infants of nursing mothers. Caffeine may also worsen incontinence or ulcers. Diabetics should take care when using green tea due to possible increases or decreases in blood sugar levels. Severe liver disease patients may experience prolonged effects of caffeine since it may build up in the blood.
Interactions
Research regarding herb and supplement interactions is lacking; however, caffeine has been shown to have adverse effects when combined with ephedrine, amphetamines, benzodiazepines, diazepam and phenylpropanolamine. Caffeine effects may be magnified when taken with disulfiram, birth control pills or hormone replacement therapy, ciprofloxacin, norfloxacin, fluvoxamine, cimetidine, verapamil and mexiletine. Speak to a qualified health care provider before using any new supplementation.
References
- University of Maryland: Green Tea
- Shixian Q, VanCrey B, Shi J, Kakuda Y, Jiang Y. (2006). Green tea extract thermogenesis-induced weight loss by epigallocatechin gallate inhibition of catechol-O-methyltransferase. J med Food. 9, 451-458.
- Phung OJ, Baker WL, Matthews LJ, Lanosa M, Thorne A, Coleman CI. (2010). Effect of green tea catechins with or without caffeine on anthrompometric measures: a systematic review and meta-analysis. American Journal of Clinical Nutrition, 91, 73-81.
- Westerterp-Plantega M.S. (2010). Green tea catechins, caffeine and body-weight regulation. Physiology & Behaviour, 100, 42-56.
- Medline Plus: Green Tea (Cameliia sinensis)
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