Thanks for the info. I'm interested in fasting just because I like to do these sorts of experiments. I fast once a year for 24 hours and I'm pretty hungry by the end... so I'm not sure I have the resolve to go through the hunger pangs much longer than that. How long do those last?

My other concern is that I run 50+ miles/week and I assume that would be impossible while fasting. I'd also be bummed about loss of muscle mass.