It is highly important to define your goals. If you want an athletic training effect (improvement for the sake of athletic performance) it is important to have the fuel you need to train hard so that you get the imporvement you're looking for. If however you're looking for an asthetic training effect (fat loss for the sake of appearance)an empty stomach cardio session is in order. To enhance the adjustment your body makes to your effort , rotate your style of cardio on a regular basis. HIT and 30+30 and hill/stair sprints and long hikes and spinning and ... mix it up, and vary the length of time you train. If you really want a training effect, try to coordinate your calorie cycling with the intensity cycling of your cardio. Can you say SHREADDED!!!
To minimize catabolism, eat immeadiately after your empty gut cardio session. Since this is early am, don't be afraid of carbs, and pour on the protein. If you're not afraid of catabolism, you can wait for up to 1 hour before having breakfast. This method will make you lethargic , maybe even lightheaded,so it is best to have something liquid when the time comes to speed up the absorption process.
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