Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans

Background: Current interest in the role of functional foods in weight cont rol has focused on plant ingredients capable of interfering with the sympat hoadrenal system. Objective: We investigated whether a green tea extract, by virtue of its hi gh content of caffeine and catechin polyphenols, could increase 24-h energy expenditure IEE) and fat oxidation in humans. Design: Twenty-four-hour EE, the respiratory quotient(RQ), and the urinary excretion of nitrogen and catecholamines were measured in a respiratory cha mber in 10 healthy men. On 3 separate occasions, subjects were randomly ass igned among 3 treatments: green tea extract (50 mg caffeine and 90 mg epiga llocatechin gallate), caffeine (50 mg), and placebo, which they ingested at breakfast, lunch, and dinner. Results: Relative to placebo, treatment with the green tea extract resulted in a significant increase in 24-h EE (4%: P < 0.01) and a significant decr ease in 24-h RQ (from 0.88 to 0.85; P < 0.001) without any change in urinar y nitrogen. Twenty-four-hour urinary norepinephrine excretion was higher du ring treatment with the green tea extract than with the placebo (40%, P < 0 .05). Treatment with caffeine in amounts equivalent to those found in the g reen tea extract had no effect on EE and RQ nor on urinary nitrogen or cate cholamines. Conclusions: Green tea has thermogenic properties and promotes fat oxidatio n beyond that explained by its caffeine content per se. The green tea extra ct may play a role in the control of body composition via sympathetic activ ation of thermogenesis, fat oxidation. or both.