So I searched around for a while but couldn't find a definitive answer (maybe there isn't one), does intermittent fasting induce ketosis? I usually IF overnight until lunch-time. I've read that sleep often induces ketosis. Am I in ketosis at the end of that fast?
The Health Correlator blog has a good table for this:
As you can see, people fasted for up to 24 hours have very slight ketone production, whereas those fasted for 2-3 days have relatively high ketone levels, but the upper end only the same as the upper end of those fed a high fat diet unfasted. I suspect that a big factor would be how much carbohydrate you're storing before fasting, which would determine whether or not you actually need to enter ketosis while asleep. From the look of the table (I can't see any more details since it's from an encyclopedia, not a journal paper) it would seem that exercising (perhaps after the end of your fast), could induce more ketosis than a short (12-24 hour) fast.
In my personal observation, fasting for 15 hours everyday for three days along side a low carb diet high in good fat, and lots of black coffee sets me into Ketosis. I also workout while still fasted.
After exercising at the very end of a 20-hour fast, I showed a small amount of ketones, even though I am not on any sort low carb diet (low calorie, but not that low) and probably consume 90% of my calories in carbs.