Fasted cardio is a common practice, but for many people, exercising in a fasted state (not eating beforehand), results in fewer calories burned. This video will let you know if fasted cardio is a good choice for you
P.S. Did you know you can read a few chapters of my diet book for free? Go to http://www.thehighfivediet.com then click order, and you can start reading it before you purchase it.