Well certainly exercise will help but I'm not quite sure how to respond to your question. Do you have diabetes? My experience has been I can exercise all I want but if I don't change my eating habits it doesn't seem to do much.
The more important thing is to know if your blood sugars are in the healthy range or not. 80-120 is the norm. You can be as skinny as a rail too and if your blood sugars are out of whack that is still dangerous.
Sit-ups and cruncxhes will help. Also lay off the carbohydrates.