Green tea extract may offer weight loss support: increased thermogenesis

OB/GYN News, Feb 15, 2004 by Nancy Walsh

LONDON -- Green tea consumption may play a role in stemming the worldwide tide of obesity, Dr. Mary L. Hardy said at a symposium on alternative and complementary therapies sponsored by the universities of Exeter and Plymouth.

One area of current obesity research involves the process of thermogenesis.

Stimulation of this process, which is controlled by the sympathetic nervous system, increases basal energy expenditure and fat oxidation.

Many plant compounds, such as catechins and caffeine in tea, exert stimulatory effects on thermogenesis, Dr. Hardy explained.

Unlike sympathomimetic drugs and ephedrine, however, green tea extracts have not been shown to increase heart rate and are not associated with adverse cardiovascular effects.

"Safety concerns with ephedrine-containing diet aids have spurred interest in safer alternatives such as green tea," commented Dr. Hardy of the Center for Dietary Supplements Research on Botanicals at the University of California, Los Angeles.

In a recent open-label trial, green tea extract AR25 (Exolise) was administered to 70 moderately obese patients for 3 months.

The mean body mass index of the study participants was 28.9 on enrollment.

Patients took two 375-mg capsules twice daily, for a total daffy epigallocatechin gallate dose of 270 mg.

By week 12, body weight decreased by a mean of 4.6% and waist circumference by 4.48% (Phytomedicine 9[1]:3-8, 2002).

The investigators noted, "Stimulation of thermogenesis and fat oxidation by the green tea extract AR25 was not accompanied by an increase in heart rate.

In this respect, the green tea extract is distinct from sympathomimetic drugs, whose use as antiobesity thermogenic agents is limited by their adverse cardiovascular effects and, hence, is particularly inappropriate for obese individuals with hypertension and other cardiovascular complications."

In another study of 10 healthy male volunteers, daily consumption of green tea extract was associated with an increase in the metabolic rate equivalent to a statistically significant 4% increase in 24-hour energy expenditure compared with placebo (Am. J. Clin. Nutr. 70[6]: 1040-45, 1999).

The original hypothesis was that the caffeine component was responsible for the observed metabolic effects of green tea, but the investigators determined that the degree of increased thermogenesis could not be explained by caffeine's effects alone. It appears that catechins and caffeine act synergistically, according to Dr. Hardy.

"Green tea is likely to be the next big thing for weight loss, but other products such as bitter orange, red pepper, and ginseng berry also appear intriguing," Dr. Hardy said in a satellite symposium. "Plants eaten in some traditional cultures to suppress appetite and improve stamina during times of famine also are gaining in popularity."

"With these traditional products you have to be a little bit skeptical, however," she added.

One product known as hoodia, which is being sold widely on the Internet, is derived from certain Kalahari Desert succulents. Indigenous peoples eat the fleshy stem of the plant as an emergency food and to stave off thirst, and limited human studies have suggested that it increases the hypothalamic sensitivity to glucose and decreases ad lib feeding.

"But I can virtually guarantee that what is being marketed as hoodia contains little or none of the actual plant, which is not easily grown," Dr. Hardy said.

Consumers should be aware of significant endangered species issues and concerns about ownership and development rights which also exist with this product, she added.

NANCY WALSH

New York Bureau