A 1999 study published in the American Journal of Clinical Nutrition looked at the effects of green tea extract on energy "burning" in humans.1 Men who took daily doses of green tea extract containing EGCg plus caffeine in an amount equivalent to that found in about 3 cups of green tea, burned about 80 more calories per day than those who didn’t take the extract. (Just taking caffeine without EGCg didn’t have the same effect.) And while 80 calories per day may not seem like much, over the course of a year that adds up to 29,200 calories, or a little more than 8 pounds lost – without making any other changes!
In a study involving animals, green tea extract actually helped prevent obesity. Two groups of mice were placed on a high-fat diet designed to ensure weight gain. At the same time, one group received green tea extract while the other did not. The mice that were given green tea extract ended up gaining 47% less weight than those who didn’t get the extract.2
In another animal study, green tea extract actually helped to reverse established obesity. In a 2005 study published in the Annals of Nutrition and Metabolism, rats were deliberately overfed to make them obese. Then they were given supplemental EGCg, which markedly decreased the amount of fat tissue in their bodies, reversing their obesity.3Why would green tea make a difference in the amount of fatty tissue one carries? The EGCg contained in the tea is believed to rev up the fat-burning effects of brown fat, send glucose to muscle tissue where it is more likely to be burned (rather than to fat tissue, where it’s more likely to be stored), and inhibit the action of fat-digesting enzymes, so that ingested fat is less likely to be broken down and absorbed by the body.
1) Dulloo AG, Duret C, Rohrer D, et al. Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans. Am J Clin Nutr 1999;70(6):1040-50.
2) Shimotoyodome A, Haramizu S, Inaba M, et al. Exercise and green tea extract stimulate fat oxidation and prevent obesity in mice. Med Sci Sports Exerc 2005;37(11):1884-92.
3) Wolfram S, Raederstorff D, Wang Y, et al. TEAVIGO (epigallocatechin gallate) supplementation prevents obesity in rodents by reducing adipose tissue mass. Ann Nutr Metab 2005;49(1):54-63. Epub 2005 Feb 25.