if you are in that heartrate range on an empty stomach you are burning through muscle, empty stomach cardio should be done in an aerobic state(you shouldn't be breathing hard at all)
here is a thread you should read on empty stomach cardio
http://forums.steroid.com/showthread.php?t=380883
also, watch these videos, they will give you a good basis for creating a diet, then once you have watched one try to create a diet and post it for critique
http://forums.steroid.com/showthread.php?t=323516