Sports drinks and other on-the-run fueling products such as gels, beans and Clif Shot Bloks were originally invented to supplement your energy intake. Your body can only take in so much energy in the form of sugar, and when you exceed that level, it causes nauseau and stomach upset. The idea is not to replace the energy lost while running but to only replenish some of what is lost. Keep track along the way, and you'll develop a recipe that works for you.