1. Green tea contains caffeine and tea polyphenols, both of which can promote metabolism and accelerate the decomposition and burning of fat.

2. Green tea can improve the body's fat metabolism rate and make it easier for the body to burn fat, thus achieving the effect of losing weight.

3. Green tea can also suppress appetite and reduce food intake, thus reducing calorie intake.

4. Catechins in green tea can promote the decomposition and excretion of fat and help reduce the accumulation of fat in the body.

In a word, green tea can promote the decomposition and burning of fat in many ways, thus achieving the effect of losing weight. However, it should be noted that green tea can not lose weight alone, but also needs to be combined with healthy diet and exercise to achieve the best results.