![]() The objective of the present study is to assess the effects of subacute ingestion of oolong tea and caffeine on energy metabolism and sleep. The effects of caffeine and tea should therefore be evaluated from two perspectives: their effects on energy metabolism and their effects on sleep. Since changes in energy metabolism was expected after caffeine/oolong tea consumption in the present study, the crosstalk between regulatory mechanisms of energy metabolism and sleep warrants our experimental design to assess energy metabolism and sleep at the same time. Furthermore, sleep and energy metabolism are closely linked through “multi-tasking” molecules such as orexin, NPY, leptin, insulin, serotonin, and IL6. The link between sleep and energy homeostasis is suggested by recent epidemiologic studies, the results of which point to insufficient sleep as a risk factor for future weight gain. Together, these findings warrant further investigation of the subacute and chronic effects of tea and caffeine consumption on energy metabolism.Ĭaffeine inhibits sleep by antagonizing adenosine receptors. ![]() ![]() Known as caffeine tolerance, the acute effect of caffeine to increase blood pressure and heart rate diminishes over 1–4 days when caffeine ingestion is continued. Importantly, in these previous studies on energy metabolism, caffeine and/or tea were ingested for only 1 or 3 days. Thus, unidentified ingredient(s) of tea other than caffeine affects energy metabolism, particularly fat oxidation. Another study found that 3 days of oolong tea ingestion increased the accumulated energy expenditure and fat oxidation over 24 h, whereas caffeine alone did not significantly increase 24-h fat oxidation. Ingestion of green tea extract increases 24-h energy expenditure and decreases the 24-h respiratory quotient (RQ). The effect of caffeine ingestion on accumulated fat oxidation over 24 h, however, was not examined in any of these four studies. Many studies report that accumulated energy expenditure over 24 h is increased by caffeine ingestion, although one study found no effect. The effects of tea on energy metabolism have been assessed in parallel with the effects of caffeine. In the course of oxidation catalyzed by endogenous enzymes, catechins are transformed to polymerized polyphenols, and caffeine is slightly decomposed, alterations that might yield benefits and/or risks on diverse physiologic functions. The various types of tea produced from a single plant species, Camellia sinensis, are distinguished by the processing technique: unoxidized tea as green tea, half-oxidized tea as oolong tea, and fully oxidized tea as black tea. The effects of subacute ingestion of caffeine and oolong tea differed from the acute effects, which is a particularly important consideration regarding habitual tea consumption. Two weeks of caffeine or oolong tea ingestion increased fat oxidation without interfering with sleep. These findings suggest a role of unidentified ingredients in oolong tea to stimulate fat oxidation, and this effect is partially suppressed in a postprandial state. The effect of oolong tea on fat oxidation was salient in the post-absorptive state. The decrease in the respiratory quotient by oolong tea was greater than that by caffeine during sleep. Caffeine and oolong tea increased fat oxidation by ~20% without affecting energy expenditure over 24-h. On day 14 of each session, 24-h indirect calorimetry and polysomnographic sleep recording were performed. During each 14-day session of the present study, 12 non-obese males consumed oolong tea (100 mg caffeine, 21.4 mg gallic acid, 97 mg catechins and 125 mg polymerized polyphenol), caffeine (100 mg), or placebo at breakfast and lunch. The acute effects of caffeine, such as increased heart rate and interference with sleep, diminish over 1–4 days, known as caffeine tolerance. Ingesting oolong tea or caffeine acutely increases energy expenditure, and oolong tea, but not caffeine, stimulates fat oxidation.
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