Green Tea Boosts Metabolism, Protects Against Diseases
WebMD News Archive
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
"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
- 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