Green Tea Boosts Metabolism, Protects Against Diseases

WebMD Health News

Nov. 28, 1999 (Atlanta) -- Unlike the American hot beverage of choice, green tea isn't available on every street corner in every city. But it's difficult to dispute the nutritional benefits of this centuries-favored Asian brew, with its powerful flavonoids and antioxidants considered capable of battling chronic diseases. Now, one group of researchers claims green tea could also boost metabolism -- and help with weight loss.

In a small study, green tea appeared to raise metabolic rates and speed up fat oxidation. "Green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content per se," says Abdul G. Dulloo, a researcher at the University of Geneva, Switzerland, and lead author of the study published in the current issue of the American Journal of Clinical Nutrition. Thermogenesis is the calories the body burns while digesting and absorbing food as it's being eaten.

The study involved 10 healthy young males, none of whom was obese but who ranged from lean to mildly overweight. Each was randomly assigned to each of three meals containing one of three treatments: green tea extract (50 mg of caffeine); 50 mg capsule of caffeine; or a placebo capsule. On three separate occasions, each spent 24 hours in a specially designed respiratory chamber in which researchers could measure energy expenditure and thermogenesis.

Those who consumed green tea extract had a 4% increase in thermogenesis, with an overall energy expenditure increase of 4.5%.

Kathleen Zelman, RD, an Atlanta-based nutritional consultant and spokesperson for the American Dietetics Association, tells WebMD that she was "not very impressed" because of the study's small number of patients and because the calorie losses were "not enough to make a difference in the life of an obese person." However, "anything we can do to boost metabolism [without using drugs] is wonderful."

The thermogenic benefits that the study cites are relatively small, Zelman says. "If you're consuming 1,500 calories, you'll be burning 60 calories, less than [what's in] a cookie. Of course, every little bit counts, but that's really a drop in the bucket."

"Green tea is emerging as a healthful drink ... more because of its role as an antioxidant," Zelman tells WebMD. Antioxidants help to prevent the formation of free radicals that cause many diseases, such as cancer. "Tea flavonoids appear to be very potent antioxidants. A significant body of research has shown that diets rich in flavonoids found in tea, fruits, and vegetables are associated with decreased risk of chronic disease and cancer, heart disease, and stroke."

Tea also contains less caffeine (as low as 50 mg per cup), while coffee has 150-200 mg per cup, which Zelman says is a safer alternative for obese people.

"All that -- in addition to the fact that tea could boost your metabolism -- is reason enough to swap out one of those cups of coffee and drink green tea," says Zelman. "You're talking to a coffee drinker here. I love coffee. But the healthful benefits ... they're speculative at best. Drink a cup of tea ... you'll actually be doing something good for yourself."

Vital Information:

• In a small study, green tea has been shown to boost metabolic rates and speed up fat oxidation.
• Calorie losses were small in study subjects and wouldn't make a big difference in the life of an obese person.
• Drinking tea can still be healthy because it contains flavonoids, which are powerful antioxidants that can help protect against cancer, heart disease, and stroke.