personally I wouldn't do AM cardio on an empty stomach, it's too catabolic and u end up losing lots of muscle if you're doing this naturally of course. L-glutamine helps, whey shake helps, BCAA's help too... I prefer to eat something and run in a couple hours though. Fat burning will occur when u finish running for some time from the elevated metabolism. Not while you're running around for a full 20-30 minutes.