>
>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.