When Coca-Cola wanted to experiment with a supposedly healthy green-tea-flavoured drink, it targeted young Japanese women first.

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"They've found people who drink green tea every day are leaner, " Tallmadge says.

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He said more research would have to be carried out before patients could be advised to drink green tea after a heart attack or stroke.

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Other studies from China showed that the more green tea patients drank, the lower their risk of developing stomach, esophageal, prostate, pancreatic and colorectal cancer, compared with those who did not drink green tea.

CNN: Five 'eating better' foods to slip into your diet in '10