Hi,
There is actually medical evidence & research that shows (in China and in the West - 1 was carried out by the house of lords) that Green tea is good for you for reducing chances of cancer, arthritis etc. but as for weight loss, I dont know. When I first arrived in China I drank a lot of Longjing green tea (as I do now) and lost a lot of weight, when I didnt drink as much my weight loss slowed down, now I am drinking more again, my weight loss has picked up, BUT I think its more to do with other factors as well rather than just the tea.
You are better off going to China town (or order over the internet) and getting something like Xihu Longjing tea if you are interested in the health benefits of teas.
Anyway, a chinese friend pointed me in the direct of this website - its interesting.
Amazing Green Tea - Want To Discover Your Next Great Tea?
Hope that helps.
xx