I have been doing 30 minutes of HIT cardio in the morning to loose fat and I have gone down 3 inches on my waist. Recently I had a one on one personal trainer and he told me that I could have been loosing muscle instead of fat. He explained that if I do cardio on empty stomach there is not much to use as fuel since I have been sleeping and not eaten for 8 hours .So when I do cardio what ever I have left will be burned quick so how will my body know weather to use fat as energy or muscle? Meaning my body could be catabolic state?
Is this wrong?