Part II - Adaptation
Phinney and Volek explain that it takes several weeks for the body to adapt to the ketosis, what they call keto-adaptation. During this period, there may be some issues like light-headedness, tiredness, etc. This is because the brain is not getting enough energy from glucose, while at the same time your body is not producing enough ketones to fuel it. They also recommend getting a device that measures your blood ketone level, so that you know you're doing it right. I got one of these:
Nova Biomedical - Nova Max Plus
The device itself is cheap, but the ketone test strips are about $2.50 each or more.
My adaptation was surprisingly quick and easy. After one week, my ketones were at 2.5 - the optimal level recommended by Volek and Phinney. I did experience some light-headedness, but this was taken care of by consuming more sodium - lots of sodium. The book recommends 2g extra per day, which is exactly what I did, in the form of bouillon. This completely solved the problem. If I skip one of the two bouillon cubes in a day, the light-headedness returns soon thereafter. In addition, I also put a lot more salt on my food than I used to, so the added sodium is really more than 2g. [EDIT 2012-09-04: I realized that one bouillon cube is two servings, and it's 1g sodium per serving, so I actually took 4g extra sodium per day, in addition to the added salt on food].
While it takes a while to get into the optimal keto-adapted state, it is quite easy to slip out of it. I had a challenge of this sort in the form of a bachelor party camping weekend, with beer tasting at the Sierra Nevada brewery. I moderated my intake of beer and other carbs significantly (which kind of sucked). In the week after, my morning ketone levels were borderline. The book recommends 0.5 or higher. My values were between 0.3 and 0.8, and the race was next Sat. Yikes.
As for the eating on a ketogenic diet, it's awesome. Not only is all the fat quite tasty, but for some reason eating is just much more pleasurable! Each meal is like a feast, even if I'm eating the same stuff I ate before.
My actual running training for the race consisted of exactly two runs. One 2.5h trail run at about a 12min/mi average pace (walked the uphills), and one 3h flat run at similar pace, where I tried to stay under 75% of max HR. Both done with no carbs, of course. The trail run felt a bit sluggish, but it was early in the adaptation period. The flat run was totally fine.