Running doesn't consume or affect hunger in any way, on any difficulty, you can run forever without any affect to the hunger bar at all. I've ran 3000 blocks, and not had even a half haunch of hunger taken away.

How to reproduce:
1. Set difficulty to hard & get a full hunger bar
2. Start running. Just run run run run run

You'll notice that you can basically run forever, without any affect to hunger. Jumping, punching, taking damage, all affect hunger however.

I created a brand new flat world on hard mode, and ran in a straight line for 3000 blocks, again with no affect to hunger.