Re: Q. for Chrisb1
Day three and the return of genuine hunger would mean that you are totally free of toxemia and where the body required no healing; plus you are deficient in certain major nutrients.
These are highly unlikely scenarios after only three days and where I have never come across this before in so short a time frame.
What you are most likely experiencing is an intense "Toxic Hunger" which should not be mistaken with the genuine article.
If the fast is continued, then these hunger-symptoms would disappear and the fast would proceed as normal.
Alternate day fasting or what most of us here refer to as IF (Intermittent Fasting) would probably leave you in a constant state of hunger as opposed to going well beyond the 3 day mark where ketosis does a very satisfactory job of suppressing hunger/appetite.
I was going to experiment with IF in the Spring but never actually got around to doing so. This Summer is a more likely option.
Regards
Chrisb1.