If you study hard, don't think too much about losing weight. On the one hand, mental work is laborious and consumes a lot of energy, which will naturally have a certain weight loss effect. On the other hand, eating less and exercising more consumes too much energy, and learning may not be able to concentrate. You are only 12 years old. Don't try to lose weight. Your health is the most important thing at this age. Don't you want to grow taller? A reasonable diet and proper exercise are enough. Study hard, learning is also a kind of exercise.