Oolong tea is semi-oxidized leaves of the Chinese camellia (Camellia sinensis ). Oolong is generally considered halfway between a green tea and a fully oxidized black tea. The taste of a good oolong should rich an floral and the tea itself should be golden in color.
We tend to think of tea simply as a beverage but it played a key role in the pharmacopeias of the Far East for centuries. It's effectiveness as a treatment for obesity and aging were cited as far back as 1578 in the "Compendium of Materia Medica" by renowned herbalist, Li Shi-Zhen. Modern medicine backs up these traditional uses. Recent studies have shown that tea consumption speeds up the metabolism in ways not attributed to the naturally occurring caffeine.
Additionally all teas from Camellia sinensis contain compounds known as polyphenols -- a class of bioflavonoid -- which are found in all plants. Polyphenols have anti-cancer, antioxidant, anti-bacterial, and anti-viral properties. Aging is, among other things the slow oxidation, of our bodies at the cellular level. Polyphenols are among those most powerful anti-oxidants.