Already lauded as a powerful antioxidant, green tea extract may also help dieters shed fat, according to researchers reporting in the December issue of the American Journal of Clinical Nutrition.

Green tea extract may also be a safe improvement on traditional diet drugs because its benefits are "not accompanied by an increase in heart rate," writes Dr. Abdul Dulloo, of the University of Geneva in Switzerland.

As part of their study, the investigators measured the 24-hour energy expenditure of 10 healthy men receiving three doses of caffeine (50 mg), green tea extract (containing 50 mg caffeine and 90 mg epigallocatechin), or a 'dummy' placebo per day.

The study authors report that, compared with placebo, treatment with green tea was associated with a "significant increase" (+4%) in daily energy expenditure. This effect was not linked to the relatively small amounts of caffeine found in tea, since subjects receiving amounts of caffeine similar to those found in green tea displayed no change in daily energy output.

Dulloo's team points out that "there are only two ways to treat obesity: reduce energy intake (i.e., dieting), or increase energy expenditure." According to their analysis, green tea extract seems to perform the latter function, although the mechanisms behind its action remain unclear.

The investigators note, however, that green tea extract contains a high amount of catechin polyphenols. These compounds may work with other chemicals to increase levels of fat oxidation and thermogenesis, where the body burns fuel such as fat to create heat.

"Stimulation of thermogenesis and fat oxidation by the green tea extract" did not raise subjects' heart rates, the researchers note. This may render green tea superior to stimulant diet drugs, which can have adverse cardiac effects, especially in "obese individuals with hypertension and other cardiovascular complications."

Sources American Journal of Clinical Nutrition 1999;70:1040-1045.