The human body is constantly burning calories.
Even when sleeping or sitting down, our cells are performing billions of functions that require energy.
Several studies suggest that green tea can make us burn more calories, even at rest.
In most studies, this amounts to about a 3-4% increase, although some studies show an increase as high as 8%.
For a person who burns 2000 calories per day, 3-4% amounts to an additional 60-80 calories per day, similar to what you might expect with a high protein diet.
Although most of the studies were very short in duration (1-3 days), there is also some evidence that the metabolism boosting effect persists in the long term.
In one study of 60 obese individuals, the group taking green tea extract lost 7.3 lbs (3.3 kg) and burned 183 more calories per day after 3 months.
However, keep in mind that not all studies show that green tea boosts metabolism. The effect may depend on the individual.