ketosis after just 36 hr in 2nd last fast - is this normal

I finished a 19 day Water Fast last month. During that fast it took me an unusally long time to show ketosis on keotsticks (5 days instead of three).
One month on I have started another fast and show ketosis after only 36 hours rather than the expected three days.
I feel fine btw but I am puzzled as to why. Did my body adapt to promoting ketosis when glucose was depleted? Is this long term change in physiology only seen in long fasts? Anyone know any the scientific/medical papers on this stuff? I am particularly interested in whether there has been an epigenetic change in genes regulating ketosis adaption.
cheers

heather