I too am twelve and know from experience that limiting yourself to one portion of only healthy foods and twenty minutes of excercise a day can help you to get a healthy weight. However if your weight is already healthy this can help you maintain it. Answer 2: Hi. First of all, you are quite young to lose weight now as you are still growing and dieting may effect that. Just eat healthy foods - 5 veggies and 2 fruits a day and do not eat too many junk food. Also exercise 15-30 minutes a day three times a week. Good luck. You should consult your parents before you do this though.