I know that someone else or a few people have discussed the issue of running in the morning with or without food preworkout, but I'm still confused. I don't want to lose my muscles along with fat when I run in the morning without eating first.

I read this book and it explained that anytime you run in the day, your body uses three energy sources: fat, carbohydrates, and protein. It didn't really explain the three but it said that when you run at a steady pace for around 30 minutes, your body burns half fat and half carbs. So you see, you do burn fat whenever you run. The book also said that when you run first thing in the morning without eating, your run will definitely be less intense and you will feel lathargic and totally like crap. I did it today and it was pretty uncomfortable, but I made it. Any thoughts on this?