Green Tea for Weight Loss
November 1, 2000 3 minutes read
Clinical Abstracts
With Comments by Adriane Fugh-Berman, MD
Green Tea for Weight Loss
November 2000; Volume 2; 86-87
Source: Dulloo AG, 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. An J Clin Nutr 1999;70:1040-1045.
Objective: To determine whether a green tea extract could increase energy expenditure (EE) and fat oxidation in humans.
Design/Setting/Subjects: Crossover study in 10 healthy men (subjects acted as their own controls) utilizing a respiratory chamber at the University of Geneva, Department of Physiology.
Treatment/Dose/Route/Duration: On separate occasions subjects were given green tea extract (50 mg caffeine and 90 mg epigallocatechin gallate); caffeine (50 mg); or placebo, which they ingested at breakfast, lunch, and dinner.
Outcomes: 24-hour EE, respiratory quotient (RQ), and urinary excretion of nitrogen and catecholamines.
Results: Ingestion of green tea extract resulted in a significant increase in 24-hr EE (4%, P < 0.01) and a significant decrease in 24-hr RQ (from 0.88 to 0.85, P < 0.001) with no change in urinary nitrogen. Norepinephrine excretion was 40% higher during treatment with green tea than with placebo (P < 0.05). Caffeine had no effect on EE, RQ, urinary nitrogen, or urinary catecholamines. No significant changes in heart rate were noted during he first eight hours the subjects were assessed.
Funding: In part by Arkopharma laboratories and by the Swiss National Science Research Fund.
Comment: Well, this should cause widespread shortages of green tea. In the Chinese side of my family—where eating combines art, sport, and religion—copious amounts of tea were considered antidotal to the semi-comatose state induced by banquets. The explanation tendered was that tea "washed the fat off the sides of the stomach." OK, maybe it wasn’t the right mechanism, but my relatives may have had a point; green tea does seem to burn calories.
This study seems to show a clinically significant difference. The authors state that thermogenesis is assumed to contribute 8-10% of daily EE in a typical sedentary man. The green tea extract increased 24-hr EE by 4%, which would extrapolate to a 35-43% increase in the thermogenesis compartment of daily energy expenditure. They didn’t calculate further, but if I am extrapolating correctly, that means that green tea could cause on the order of a 3% increase in daily EE.
Caffeine is known to be thermogenic (and, for some of us, life-sustaining), but not in the doses used in this study, which the authors admit; only doses of caffeine > 100 mg can cause a thermogenic effect for 1-2 hours, and 600-1000 mg/d is necessary to affect 24-hr EE in the respiratory chamber. The dosage of caffeine was reasonably chosen to equal the amount in the green tea extract, and this experiment does demonstrate that green tea has some thermogenic qualities that are not caused by caffeine alone. One possible explanation is that flavonoids, called catechins, in tea inhibit COMT, the enzyme that degrades norepinephrine (which helps to control thermogenesis and fat oxidation).
Capsaicin (the compound that provides the heat in chili peppers) has also been shown to stimulate thermogenesis and fat oxidation in humans, but that’s probably obvious to anyone who has doffed a jacket and mopped a brow after a good curry. So hot food and green tea may be a good combination for those watching their weight.
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