Running five miles before breakfast is more than just a habit; it is also a skill. Many people simply can't run 5 miles right now, they need to first train up to acquire the ability to do it.
All this of course depends on the individual's physiology and psychology.
For me, I tend to run either before breakfast or in the wee hours of the morning (one/two o'clock) before going to bed.
Mind, I'm an ultra runner, where being hungry and sleep deprived for days is the name of the game, so I've overcome that particular psychological barrier.