Probably not. But green tea extract does make mice stronger swimmers, Japanese researchers report. Ten weeks of green tea supplements plus strenuous exercise made mice swim longer and stronger than mice that swam their laps without performance enhancement.
"We have shown that green tea extracts are beneficial for improving endurance capacity, and that this effect is accompanied by a stimulation of [fat] metabolism," Takatoshi Murase, PhD, writes. "Although the clinical efficacy of green tea extract has not yet been confirmed in human studies, our results suggest that green tea extract may be a useful tool for improving endurance capacity."
Even better news: The mice got stronger because the green tea made them burn fat more efficiently, suggests Murase and colleagues at the Biological Sciences Laboratories of Kao Corp., Tochigi, Japan. Kao Corp. is a maker of green tea products.
The findings appear in the online edition of the American Journal of Physiology: Regulatory, Integrative and Comparative Physiology, published by the American Physiology Society.
Mice — even mighty mice — are not men. But Murase calculates that the amount of green tea eaten by the mice would work out to about 4 cups of green tea a day for a 165-pound human athlete. That's a little less than a liter of tea a day.
Green tea does contain caffeine. But evidence indicates that the performance enhancement comes from green tea chemicals called catechins and not caffeine. The main catechin in green tea is called EGCG. Taken by itself, EGCG did enhance mouse performance. But this effect is "weak," Murase says, compared with the effect of whole green tea extract.
Sources: Murase, T. American Journal of Physiology: Regulatory, Integrative and Comparative Physiology, online edition, January 2005. News release, American Physiology Society.
By Daniel J. DeNoon
Reviewed by Michael W. Smith, MD
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