A recent study in the American Journal of Clinical Nutrition found that research subjects who drank green tea as part of a controlled diet saw an increase in metabolic rate. The authors concluded that 3 or 4 cups of green tea could increase metabolic rate by 4% over 24-hours. That translates into burning an extra 50 to 100 calories a day. There is still need for more human studies to understand how green tea works, but drinking green tea certainly can't hurt. Read about the health benefits of green tea from the Guide to Japanese Travel at About.com.