If you've been eating a low-fat, balanced diet consistently, and have been doing aerobics 3-4 times per week, but you still aren't getting the results you'd expect, you may want to check the intensity of your aerobic sessions. For maximum benefits, you must train continuously for 20-60 minutes per aerobic session in your target heart rate zone.
 
The activity can be anything you choose that raises and maintains your heart rate to the training zone for 20-60 minutes. But you should check your heart rate periodically to make sure you are in your training zone. Don't cheat by "taking it easy" for 10 minutes, then sprinting for 30 yards and then taking your heart rate! Your heart rate should be steadily maintained in the zone for the entire 20-60 minute aerobic session for maximum effectiveness.