NEW YORK, Nov 22 (Reuters Health) -- There's good news for dieters: green
tea appears to speed up calorie burning, including fat calorie burning,
researchers report.
"The green tea extract may play a role in the control of body
composition," Dr. Abdul Dulloo, of the University of Geneva in Switzerland, and
colleagues write in the November issue of the American Journal of Clinical
Nutrition.
Dulloo and colleagues studied the effects of green tea on 10 healthy young
men, average age 25, who ranged from lean to mildly overweight. For 6 weeks, the
men took two capsules at each meal: green tea extract plus 50 milligrams of
caffeine; 50 milligrams of caffeine; or a placebo (inactive capsule).
The study participants were on a weight-maintenance diet of about 13%
protein, 40% fat, and 47% carbohydrates, a "typical Western diet." Three times
during the study, the men spent 24 hours in a special room where the
investigators measured their respiration and energy expenditure.
Energy expenditure -- the number of calories used during a 24-hour period
-- was higher for men taking green tea extract than for those taking caffeine or
placebo, the authors note. They also found evidence that men taking the green
tea extract used more fat calories than those taking the placebo.
There was no difference between the caffeine users and the placebo users
in terms of either overall calorie burning or fat calorie burning. Dulloo's team
therefore concludes that the increased calorie burning in the green tea group
cannot be explained by caffeine intake alone.
The study authors suggest that the caffeine interacted with natural
substances in green tea called flavonoids to alter the body's use of
norepinephrine, a chemical transmitter in the nervous system, and increase the
rate of calorie burning.
The researchers point out that, unlike some diet products, green tea does
not contain high doses of caffeine, and it did not affect the heart rate in the
study participants.
