Cardio (cardiovascular exercise) is a crucial part of any healthy lifestyle, tut there is such thing as TOO MUCH cardio!
Yes indeed, believe it or not, doing too much cardio can actually keep you from achieving your weight loss goals or desired physique. Too much cardio increases the cortisol in your body which can tear down your muscle tissues. The less muscle you have, the slower your metabolic rate. Essentially, you are running yourself OUT of shape. So take it easy on the treadmill!
While everyone is different, I limit my cardio workouts to about 30 minutes, 3 or so times a week. For your health and belly, give cardio a rest every now and then.