I read an article in the June issue of Running Times that suggests for marathon training, some think it may be better to not take GU or other solids during long training runs. That way, your body can adapt to glycogen depletion and more efficiently burn fat instead of carbs, etc. In any event, that advice is contrary to most of the training advice I've seen (e.g. Pfitzinger's Advanced Marathoning). Those other sources describe the same glycogen depletion phenomenon, but they suggest GU or other solids during long training runs. Certainly the consensus is to take GU or solids during the actual marathon. Thoughts on whether to take GU or other solids during long (18 mile+) training runs?