There actually have been studies done that show you burn fat 300% more efficiently on an empty stomach (e.g- fasted state, first thing in the morning).

My last 4-6 weeks in precontest mode I do cardio 3 x's per day - every 8 hrs. - 1st session is fasted then midday, then 1 hr before bed.

By doing this you're hitting your system with a boost of adrenaline every 8 hrs from increased heart rate, plus you can increase intensity for a shorter period and don't have to stay on a treadmill or stairmill for 1.5-2 hrs at a time. Took me 15 years to devise that cardio regimen and works like a charm while not burning muscle in the process.