I find that the most energy I have for running comes after having fasted - so if I skip breakfast and lunch and then do an afternoon run or ride, I'm basically on fire for it. Not that I fast a lot, but when I do that's the result.
On a clean primal diet you can do basically jack all in terms of exercise for ages and then still be capable of performing. In evolutionary terms, that's the ideal physiology to have really - you conserve energy for the most part, but you can also 'put the hammer down' at a moments notice. That's why I never really plan any training, I just do is when I feel like it.
Healthy is the new wealthy.