Originally Posted by lostinthesaus
Why don't you just try both and see what works best for your body type?
Because they're both awful ideas.
When you get up in the morning, your cortisol levels are very high. This is a very catabolic state for any sort of exercise; breakfast is tremendously important because it gives your body something to use for fuel aside from burning muscle. Doing fasted cardio in the morning is a great way to lose tons of muscle unless you have the rest of your diet completely dialed in.
Get up, eat some oatmeal and a couple eggs, and do your cardio. You'll have better endurance and a much better workout overall.
If you're going to be lifting, same story. You need fuel for your muscles, so why try to go lift on an empty tank? Having not eaten does NOT mean you'll burn fat. Muscle is the most metabolically expensive tissue and is the first tissue to be broken down for energy.
Also, you need to eat immediately after you finish exercising. Get some protein and carbohydrates so that your body can start repairing all the microtears you've created in your muscles. Remember, this rebuilding process is what causes the muscles to grow! I keep taking for granted how much people know; I'll write up a good post-workout nutrition sticky for everyone to peruse.