My first question is 'who David Roche' that there is 109 pages, so I had a quick look at last page. Still don't don't know.
But haven't we gone full circle, from Lore of Running and before. Basic biochem and physiology 'tell you' why carbs are essential for high (fast) performance, not so much for ultras. You seen many thin ultra runners (plodders) recently?
A good low 2hr marathoner , light and muscular enough, can actually carry his glycogen pre stored for the whole race requirements. The serious weekend warriors, sub 3 and maybe 4 do need in race fuel, and fat aint going to cut it. However, assuming from title, if you are talking Western States (not going to read 109pages), you don't even need carbs except some glucose for the brain.
But we are not re-inventing what humans have been doing 1000's of years , except that early hunters never exercised fast, their chases were extremely slow, waiting for prey to collapse. Running faster, for longer required more glucose. I digress.
But...here is the longer term problem. Many older runners used to such diets, suddenly find themselves pre diabetic and diabetic with skinny fit bodies. What the...yep. Keep pushing your physiological boundaries and systems start rebelling. Insulin starts behaving not the way it was meant to but on the expectations you have put it through for many years. Use it...or lose everything. Not a game of chance, because you had the inputs.
cheers