One way I can tell when I'm in ketosis...
Whenever I hit ketosis, my body temperature seems to drop. It has nothing to do with fasting specifically, but just the general state of ketogenesis. I can fast for 24 hours after a reefed and still not be in ketosis and body temp is normal. Or I can eat a high fat meal and enter into ketosis, and bam, body temp drops.
When I'm in ketosis, I get cold all over. Not, like, unbearably so, but it's definitely noticeable. I've noticed this for a while, and it seems to be a pretty reliable indicator.
Am I the only one that has noticed this? I wonder if it means anything. :p