If you are a boy, you can't lose weight, because your figure is the thinnest at this stage. No matter how thin you are, you can't lose weight. You may lose a few pounds, but your body looks better than before. If you think you are fat, it's because there is a little fat covering your abdominal muscles. After exercise, you won't feel fat.

If you are a girl, you can lose at least 10 kg after running for one month. The most important thing to lose weight is not only exercise, but also eating.