I stay low carb (<25 gm/day) before, during and after bike marathons and my father (now age 65) has been running marathons for decades and never eats anything during runs, only water. What I understand is that if you let your body rely on glucose (carbs) then it will always want glucose. Unfornately, you can become dependent on that glucose. If you train your body to run on fat-burning, you can get down to some really low body-fat percentages (even as low as 4%) and still have fuel to spare.