green tea (in extract) with that of a placebo, researchers found that the green-tea drinkers burned about 70 additional calories in a 24-hour period. If you can believe it, those 70 calories a day add up to a total of 7.3 pounds of fat a year! It's not magic, it's science: Researchers believe the difference is caused by metabolism-enhancing antioxidants known as catechins, which are found in green tea.