There are two ways to exercise: to create muscle which also increases metabolism so that you keep off the weight, try strength exercises and do cardio at a high heart rate (say 160bpm). To lose weight, surprisingly, lower the cardio heart rate so that you don't exceed 120bpm.

My two cents: I've found that if I'm exercising regularly, I don't crave poor nutrition foods. I think it gives me natural energy so that I don't seek it subconsciously in sugary or fatty foods.