> >One very interesting thing about running low carb is that I never seem >to run out of energy on a run. I do get tired of course, but never feel >like I do when running on a high carb diet, where I would suddenly go >flat. I haven't run a marathon since high school, no interest, but I >think I could train for one and run it without too much trouble. This has been my experience as well. I followed the 'standard endurance athlete' diet for years (lots and lots of carbs) while doing ultra's (50Km of greater), adventure races, etc. I would hit that 'flat' spot at about 1 to 1.5 hours, and after that it was GU's (pure gel-type carbohydrate) and power bars to keep going. On a paleo diet (although I don't consciously attempt to limit carb's, but eat far fewer carbs than before), I never hit that wall. One caveat is my endurance activities have been limited to a max of 2-3 hours since I went paleo. Bottom line for me is I feel better, and although less important for me now, perform better, doing these mid distance activities on paleo.