I never used to be able to function, let alone run in the morning - I really struggled with breathing, stitches, and my legs felt so heavy. Since getting my dogs I take them out for their walk first thing, so I just got used to walking a reasonable distance first. Now I combine the two - I run with them, and my morning running is my preferred time. I usually run 3-6 miles a day. I think it's something you can condition yourself to, but up to certain distances. Above that, you do need some food inside you.