How fast your heart beats after running determines whether you can lose weight. Generally, the heartbeat is around 120, which will have the effect of losing weight. Low will increase endurance, high will increase explosiveness. Generally speaking, the best way to lose weight is jogging 100 and running 300, which is the most effective way to go back and forth. Remember to eat less, especially greasy food. Three months, 20 pounds less, should be no problem.