No. A calorie controlled diet and healthy food choices are absolutely essential to losing weight around the waistline or anywhere else. Exercises can tone muscle, strengthen muscle and even build muscle size, but they will do very little to change body fat. Also, 20-30 minutes 4 times a week won't be enough to see big changes fast, but if kept up over a long time, they can help you feel healthier, stronger, and more in control of your body.