Quote Originally Posted by lstbred
Dont want to de-rail, but what major dif do you find doing it fasted?
Since you're operating on a caloric deficit first thing in the morning and there typically are fewer carbohydrates available for energy, a moderate intensity cardio on an empty stomach utilizes/burns fat more efficiently. "Fasted" cardio puts you directly into oxidative phosphorylation which feeds off fat stores. When fasted from sleep your body already has used a lot of your glycogen stores so you can utilize fat instead. Cardio after eating just allows you to burn off the carbohydrates you've ingested and then your glycogen stores.

I wouldn't recommend HIIT cardio on an empty stomach because HIIT uses more glucose for fuel and on an empty stomach you are limited in intensity output.