The leaves have a lipolysis activity.  The caffeine content promotes draining of the fat outside the adipose tissue (fatty cells), by enzymatic stimulation, the triglycerides that are stored are then mobilised as free soluable fatty acids and are easily eliminated by the body.  

The polyphenol content in green tea permits a progressive liberation of the caffeine, avoiding sleep and nervous problems and can also decrease the assimilation of food carbohydrates and lipids, so it limits calorie intake.