Green tea extract: The next big boost to weight loss

November 21, 1999

In addition to its potential cardioprotective action, green tea extract may serve as an aid to weight loss: in clinical trials it appears to raise metabolic rates and speed up fat oxidatin. Dulloo and colleagues at the University of Geneva, Switzerland, demonstrated that in addition to caffeine, green tea contains catechin polyphenols that raise thermogenesis (the rate at which calories are being burned) and overal energy expenditure. This metabolism-boosting effect seems to be independent of the supplemental caffeine the study's subjects consumed.

None of the ten healthy young male subjects were obese, ranging from lean to mildly overweight, and none of them was dieting during the study. A typical American non-weight-loss diet averaging 40% fat was prescribed during the course of research, and subjects were randomly assigned to each of three meals containing one of three treatments: green tea extract containing 50 mg of caffeine; 50 mg capsule of caffeine by itself; or a placebo capsule. On three separate occasions each subject spent 24 hours in a specially designed respiratory chamber in which thermogenesis and energy expenditure were carefully measured. When gauged by these relatively sedentary circumstances the subjects' thermogenesis showed a 4% increase, and overall energy expenditure increased by 4.5%.

Although millions of cultures throughout the world consume coffee and tea, only coffee's effect on fat metabolism--by virtue of its caffeine content--has been widely studied. But caffeine's increase of metabolic rates has only been noted at much higher doses than the 150 mg/daily of this study, which is barely the amount in one cup of brewed coffee. And since caffeine is known to increase heart rate, green tea appears to provide a safer alternative for obese patients who may have hypertension or other cardiovascular problems. Of particular interest in this sutdy is the fact that subjects who received only caffeine--not green tea--showed no change in their metabolic rates. Rather, the authors propose a synergistic interaction between caffeine and other bioactive ingredients in the green tea extract which helped to promote a higher rate of fat burning.

Dulloo A G 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: 1040-45.

American Journal of Clinical Nutrition

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