While most people are already aware that oolong tea is good for the health, a monthlong experiment by a Japanese doctor has proved the tea reduces body fat and rejuvenates internal organs, thanks to the fact it contains a large amount of a substance called polyphenol.

"I never expected to get the result I wanted from this experiment in such a short period of time," said Masatoshi Nakano, a lecturer at an Aichi Medical University institute.

In April, Nakano asked 12 men and women aged between 18 and 39 to participate in an experiment to examine the effect of oolong tea on their health. All the participants had a clean bill of health and a body mass index of between 20 and 30.

The participants were effectively asked to soak their lives in oolong tea for a month. They were required to drink at least one liter of oolong tea each day and refrain from drinking water. Participants were also asked to eat a balanced diet during the period. Blood samples were taken from the participants for analysis both before and afterward.

The tea used in the experiment was a brand commonly available in PET bottles at shops.

After the experiment, Nakano took the blood samples to Yasuharu Mitomo, a professor at Nagoya City University, and asked him to examine them. Mitomo is known as a pioneer in the study of "internal-organ aging." Using various indicators, such as cholesterol and blood sugar levels, and hepatic (liver) activity, he has been researching the impact of different lifestyles on the aging process of internal organs.

In testing the blood samples, Mitomo used a calculation method he devised for evaluating the age of organs. He used the results of medical checkups as the basis for the calculations.

Comparison of the blood samples produced what appeared to be remarkable results. The internal organs of the participants were rejuvenated by an average of 1.9 years and a maximum of nine years. The average age of the 12 was 26.9. Before the oolong tea experiment, their average internal organ age was 30.3, which dropped to 28.4 after the experiment.

The one whose internal-organ age was rejuvenated by nine years was a woman aged 29. Her cholesterol level fell from 206 before the experiment to 157 afterward, while her LDL--or level of so-called bad cholesterol--sharply dropped from 137 to 98. Along with the decrease in cholesterol levels her overall internal-organ age dropped from 38 to her actual age of 29.

"The higher the combined level of cholesterol, the harder your arteries become," Mitomo said. Hardening of the arteries is believed to be a common cause of fatal heart attacks and strokes.

The combined cholesterol levels of most of the participants fell, as did their g-GTP--an indicator of hepatic activity. Meanwhile, HDL--a measure of good cholesterol--rose in many cases.

"Although I want to see more results in three months or so, the dramatic improvement in these figures over such a short period of time is extremely interesting,"Mitomo said.

The result of the experiment also showed that oolong tea helped to reduce body fat during the test period. Nine of the subjects saw a two-centimeter reduction in their waist size, while eight also saw the size of their upper arms reduced by two centimeters.

According to Nakano, oolong tea helps the body burn fat more efficiently than other teas, including green tea and black tea. It also helps reduce the buildup of body fat.

It has long been believed that oolong tea, which is a good accompaniment for greasy Chinese dishes, helps people lose weight. However, this is the first time a study has found conclusive evidence to support the claim.

Nakano intends to present a paper on the findings to the Japan Society for the Study of Obesity in October.

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Polyphenol in oolong tea

So how does oolong tea achieve this effect?

"The effect is a result of the polyphenol contained in oolong tea," Nakano said.

Those familiar with polyphenol probably tend to associate it with red wine--the red wine boom in Japan over the past few years has actually been a polyphenol boom. The substance is also contained in many other foods, such as blueberries. There is even polyphenol in some brands of chewing gum.

"You talk about polyphenol, but there are actually thousands of kinds," Nakano said. "They can all stop hardening of the arteries to some extent, but it's the size of the polyphenol molecules in oolong tea that's so remarkable."

He said the molecules form a perfect match with hormone-sensitive lipase, an enzyme that dissolves body fat. This match activates the enzyme.

The size of polyphenol molecules varies from tea to tea depending on the level of fermentation. In the case of green tea, which does not go through the fermentation process, the size of the molecules is half that of oolong tea. In the case of black tea, which is fully fermented, the molecules are about twice the size of those in oolong tea. Therefore, neither green tea nor black tea can dissolve body fat to the same degree as oolong tea, which is only half fermented.

Oolong tea is available in a variety of forms from familiar PET-bottle brands to neatly packaged, high-quality tea leaves.

"If tea leaves are not stored properly and get exposed to too much sunlight, they ferment faster. It's also possible that tea leaves fermented to different levels end up getting mixed together. So perhaps high-quality leaves that have been stored properly are the most effective," Nakano said.

Ultimately, though, gulping down gallons of oolong tea alone will not keep you trim.

"While it's true that oolong tea dissolves fat efficiently, you also need to consider keeping a balanced diet," he said.

"Polyphenol is contained in more or less every plant, so to avoid hardening of the arteries you don't necessarily have to drink oolong tea, you could just eat a lot of vegetables," he added.

From Yomiuri.co.jp