Originally Posted by PDKL45

The guy was still adapted to burning carbohydrates, rather than fat. If he was properly in ketosis he could have done a hard effort burning fat. If--and the big thing here is that if--you are properly in ketosis, you can go as hard as you like, provided you take on sufficient fat to power the effort.

Ketosisis in no way a ridiculous premise, it's merely the body adapting itself to utilize fat, rather than carbohydrates, for energy. I know someone who rode a couple of 200K brevets drinking from a bottle of olive oil, just to prove that it could be done, to himself as much as anyone.