All tea is derived from the leaves of the Camellia sinensis plant, but the leaves can be processed in a number of ways that alters their final chemical composition. Fermenting the tea leaves produces black tea and drying the leaves produces green tea. However, a partial fermentation produces oolong tea with a chemical composition somewhere between that of black and green tea. Tea has a beneficial effect on obesity because it contains caffeine. However, tea shows benefits beyond that which you would expect from caffeine alone. Evidence suggests that the polyphenols contained within tea elicit anti-obesity effects in those who drink it regularly. One way that tea polyphenols may reduce weight gain is by their ability to prevent the absorption of macronutrients. Of particular interest is the possibility that they may inhibit lipase activity and prevent the absorption of fat.
Research published in the European Journal of Clinical Nutrition1 in 2006 investigated the effects of polyphenol-enriched oolong tea on the absorption of lipids in humans. A double-blind placebo controlled cross-over deigned study fed 12 healthy men and women around 38 grams of fat and a 750 mL beverage containing polyphenol enriched tea or a placebo for each of three meals. Blood tests were performed throughout the treatment period, and at the end of the treatment faeces samples were collected to test for the presence of lipids. The results showed that in the polyphenol-enriched oolong tea treatment group, the excretion of lipids (19.3 gram per 3 days) were significantly higher that the control group (9.4 grams per 3 days) In addition cholesterol excretion was higher in the treatment group than the placebo group, although this was not statistically significant.
The difference in the excretion of lipids between the treatment and control groups were 3.3 grams per day which equates to 29.7 kcals per day. This suggests that one of the mechanisms by which oolong tea is able to reduce weight gain is via a reduction in the absorption of lipids in the intestine. The proportion of lipids in the faeces was 13 and 21 % for the control and treatment group respectively. This study also found that total faecal excretion of fat was 3.1 grams per day, which supports previous findings that have reported faecal excretion to be 3 to 5 grams per day. Green tea have previously been reported to reduce the absorption of carbohydrates during test meals and so it is possible that total calorie reduction might be higher than the fat content alone suggests.
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