Green tea does indeed increase metabolism by creating a thermogenic effect in the body. It will increase resting metabolism by approximately 4% over a 24 hour period. However, you have to drink quite a bit of it to get this effect. Roughly 10 cups of tea are required to notice any metabolic side effects. You could do what many of us do if you don't want to drink tea all day and take the extract that comes in pill form. One capsule will typically contain the equivallent of 10 cups of tea and have no caffiene.

BTW, the active ingredient in Green tea is not the caffeine. It is believed that the catechin-polyphenols found in green tea are what effect the levels of norepinephrine in the body causing energy to be wasted and therefore more to be required. Look for an extract that is standardized to at least 60% polyphenols.

If you choose to drink the tea be sure you get a caffinated blend, as the decaf is much weaker than the regular. And never add cream or milk as this will negate the thermogenic effects.

All teas and coffees contain some carbs / calories - but very few. If you use the carb counter tool on this forum (under LC Tools atop every page in orange highlight) you can get an exact count for various types of teas and coffees.

HTH
Nat