Green tea is more than just hot, flavored water. The bioactive substances in the tea leaves dissolve in the water and make it into the final drink.
When you drink a cup of quality tea, you’re actually getting a large amount of beneficial substances with potent biological effects. The best known of these is caffeine. A cup of green tea contains much less caffeine (24-40 mg) than a cup of coffee (100-200 mg), but still enough to have a mild effect.
Caffeine is a well known stimulant that has been shown to aid fat burning and improve exercise performance in numerous studies. But where green tea really shines is in its massive range of antioxidants… being loaded with potent antioxidants called catechins.
The most important of these is EGCG (Epigallocatechin gallate), a substance that can boost metabolism. Keep in mind that these benefits can be derived both from drinking green tea as a beverage, as well as taking green tea extract as a supplement. Most of the studies used extracts.