Carbs are generally more of a requirement for insulin treated diabetics as we tend to have a greater risk of hypo during exercise.
You'll probably find that you won't need a great deal (if any) carbs for the majority of runs you do - but you may need some extra carbs before a long run so that you don't "hit the wall" too soon.
It's best to see what/how much exercise you can do on your current diet plan. If you're finding a severe lack of energy then you could try increasing your pre-workout carb intake. The issue is the fine line between having enough carbs to complete the big run but not too much as to make a mess of your BG levels...
You could always try increasing your fat intake as well for energy if you find you don't have enough for longer/harder workouts?
Grant