Oolong tea is produced by a partial fermentation process that results in a tea somewhat halfway between green tea and black tea in chemical composition. Because oolong tea is not fully oxidised during processing, it retains many of the flavan-3-ols present in green tea that have been linked to health benefits (figure 1). Oolong tea is mainly drunk in Southern China, where it accounts for around 2 % of worldwide consumption, but is also commercially available in Western nations from specialist health food shops. The Chinese believe that oolong tea is beneficial to the proper control of body weight. Studies have demonstrated that caffeine is effective at increasing fat oxidation and resting energy expenditure, and interest has grown in the flavon-3-ol epigallocatechin gallate (EGCG) because research suggest that it can cause weight loss in subjects who consume it regularly.
Figure 1. Analytical composition of oolong tea consumed in study by participants1
To test the weight loss effects of oolong tea, a group of researchers took 12 subjects and gave them a number of different beverages; water, full-strength oolong tea, half-strength tea or water containing 270 mg of caffeine1. The water containing caffeine treatment had an equivalent caffeine content to the full strength tea. Subjects consumed each of the drinks for three days, and on the third day their resting energy expenditure was tested in a calorimetry room by indirect calorimetry. The results showed that subjects had an increase in energy expenditure of 2.9 and 3.4 % when they consumed the full-strength tea and caffeinated water treatments respectively. The half strength tea did not significantly raise the energy expenditure above the water only treatment. Fat oxidation was 12 % higher when subjects consumed the full-strength tea compared to water.
Evidence is mounting within the scientific literature that tea is able to control body weight gain in subjects who consume it regularly. Tea contains caffeine, theobromine and theophylline, a group of related methylxanthines that may raise resting energy expenditure. However, studies show that green tea possesses weight loss effects above and beyond that which can be attributed to the methylxanthine content. Researchers have highlighted EGCG as a possible candidate for this effects, and studies show that EGCG can cause weight loss when given as an isolated supplement. It is recommended that tea is consumed regularly, because as well as its weight control effects, it has been shown to contain polyphenols that are able to protect from both cancer and cardiovascular disease. Green tea and oolong tea are the best choices because of their higher content of flavon‑3‑ol flavonoids.
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