if you are consuming enough calories in the day you wont go catabolic during cardio... if u are eating 3000 caloires to maintain your weight,doing 30mins cardio in the morning before food will only deplete you of glycogen in the muscle,so the "muscle loss" is just water loss from the muscle, you can have a meal before cardio or u can do it empty belly,i get my guys to do empty belly.
remember dont cut calories to much and dont over do the cardio as this will force u into over training and slow down the metabolism, rather adjust your macro nutrients first so if u are having 30% protein 50% carbs and the 20 % fats rather adjust those first and still keep to the 3000 caloires,add in 20-30mins cardio each day and then when weight loss slows then adjust caloires again or add in more cardio.
