According to traditional Chinese belief, oolong
tea is effective in the control of
body weight. Few controlled studies, however, have been conducted to measure the impact of
tea on energy expenditure (EE) of humans. A randomized cross-over design was used to compare 24-h EE of 12 men consuming each of four treatments: 1) water, 2) full-strength
tea (daily allotment brewed from 15 g of
tea), 3) half-strength
tea (brewed from 7.5 g
tea) and 4) water containing 270 mg
caffeine, equivalent to the concentration in the full-strength
tea treatment. Subjects refrained from consuming
caffeine or
flavonoids for 4 d prior to the study.
Tea was brewed each morning; beverages were consumed at room temperature as five 300 mL servings. Subjects received each treatment for 3 d; on the third day, EE was measured by indirect calorimetry in a room calorimeter. For the 3 d, subjects consumed a typical American diet. Energy content of the diet was tailored to each subject's needs as determined from a preliminary measure of 24-h EE by calorimetry. Relative to the water treatment, EE was significantly increased 2.9 and 3.4% for the full-strength
tea and caffeinated water treatments, respectively. This increase over water alone represented an additional expenditure of 281 and 331 kJ/d for subjects treated with full-strength
tea and caffeinated water, respectively. In addition, fat oxidation was significantly higher (12%) when subjects consumed the full-strength
tea rather than water.