I've played with ketosis. You can verify your body is in a state of ketosis using "keto sticks" that you pee on. They change color and prove that your body is outputting ketones. That's also what causes your breath to smell like something died (my wife's comment).

One of the leading thinkers on this is Tim Noakes who has written some excellent literature on the subject and is a keen runner. He became famous for "Lore of Running" which is a tome of a book but is an excellent primer for any runner serious about nutrition and metabolic processes.

Noakes has more recently joined the low carb/low GI movement and has some pretty radical thinking in the area.

I would also echo some other commenters here that Ketosis is IMHO not a healthy state and can have quite far reaching health consequences. One of the by products of ketosis is acetone which is what makes your breath smell - so there are some fairly radical changes in your body's chemical functioning as it goes into starvation and survival mode.

I tend to gravitate away from radical experiments like this and more towards what the leading edge professional athletes are doing, minus the steroids. They have plenty of motivation to innovate in the field in a sustainable way.