Green tea has thermogenic properties and promotes fat oxidation; these properties are not explained by its caffeine content alone.
Green tea extract may affect body composition via the sympathetic nervous system's activation of thermogenesis, fat oxidation, or both. On 3 occasions, 10 healthy men (mean age = 25[pm]1 years, mean body mass index = 25.1[pm]1.2) underwent measurement of 24-hour energy expenditure (EE), respiratory quotient (RQ), and urinary excretion of nitrogen and catecholamines in a respiratory chamber. On the 3 occasions, subjects received capsules containing green tea extract (50 mg caffeine and 90 mg epigallocatechin gallate), caffeine (50 mg), or placebo in random order; doses were equally divided among 3 meals.
Green tea extract also contains other catechins but epigallocatechin gallate constitutes [geq]50% of the total and is believed to be the most pharmacologically active. Compared with placebo, treatment with green tea extract significantly increased 24-hour EE (+4%) and significantly decreased mean 24-hour RQ (from 0.88 to 0.85) without any change in urinary nitrogen excretion. (The decrease in RQ reflects an increase in oxidation of fat relative to carbohydrate.) Compared with placebo, treatment with green tea extract resulted in higher 24-hour urinary norepinephrine excretion (+40%). Treatment with caffeine alone had no effect on EE, RQ, or urinary excretion of nitrogen or catecholamines.
1) Standardized green tea extract (containing 375 milligrams total catechins and 150 milligrams of caffeine) 2) 150 milligrams of caffeine 3) Placebo