I want to lose belly fat i am 20 and 49 kg 161 cm?

You are: In the low normal weight range for your age with a bmi of 18, 9 -- but if you want to lose belly fat it's the same as anyone else. Less food and more exercise. However, you don't get to choose from where your body pulls the fat you burn up, it can just as likely come from breast, buttocks, etc.

Agree w Dr. Sneid.: Spot fat loss does not occur naturally. By losing weight in general a certain amt will be abdominal fat. Eat healthfully ; be physically active. Calories burned must > calories consumed. To tighten ab's do crunches, reverse crunches, exercise ball crunches, pelvic thrusts, lying leg raises, side bridge ; “bicycling” exercise on your back. Get regular aerobic exercise.