Tea from the leaves of the Camelia sinensis plant is one of the most widely consumed beverages worldwide. Its consumption is associated with a variety of beneficial health effects. Findings from a recent study suggest that oolong tea consumption promotes weight loss.
Many types of tea from Camelia sinensis exist, but they are generally classified as green, oolong, or black. The differences in the three types arise during processing, where they undergo various degrees of oxidation. Green tea is unoxidized; oolong tea is partially oxidized; and black tea is fully oxidized. Tea contains several bioactive compounds, including catechins and caffeine. Catechins are polyphenolic compounds that exert antioxidant properties. Caffeine is a potent stimulant.
The intervention study involved 12 healthy non-obese men between the ages of 20 and 56 years. The participants consumed one of three beverages at breakfast and lunch for three 14-day sessions: oolong tea containing 51.8 milligrams of caffeine and 48.5 milligrams of catechins; a beverage containing 51.8 milligrams of caffeine; or a placebo beverage. A washout period of about two weeks separated each session. The men drank no other beverages containing caffeine or alcohol during the study period. They underwent 24-hour indirect calorimetry to monitor their metabolism and polysomnographic sleep recording to gauge their sleep quality.
The authors of the study found that fat oxidation increased by roughly 20 percent when the participants drank the oolong tea or pure caffeine beverage, but not when they drank the placebo beverage. The effects of consuming oolong tea continued to a greater degree while the participants were asleep. Neither of the caffeine-containing beverages promoted an increase in the men’s energy expenditure, and none of the men exhibited alterations in sleep quality, suggesting that they developed a tolerance to the stimulatory effects of caffeine.
These findings suggest that oolong tea stimulates fat oxidation, especially during the overnight fast.
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It’s a shame the news release omitted the dose and timing, which of course are crucial details for making sense out of this study. So I looked it up in the paper’s methods section:
The subjects either drank one can (350 ml) of pre-brewed tea containing ~50 mg of caffeine or took a 50 mg capsule caffeine both at breakfast and at lunch time. This is a really low dose and well below habitual caffeine intake for most indiviuals in Western societies. Moreover, giving the timing, it should hardly come as a surprise that it didn’t negatively affect sleep quality. Even slow metabolizers of caffeine should have completely metabolized that 50 mg taken in at lunch time by the time they go to bed!