I am looking at all of the questions asked by researchers on the long term effects of the diets and the fact that most are unanswered and call for further research.
In ancient times, our ancestors (especially and definitely pre agriculture) would have been in and out of ketosis every few days or at least a couple times a month in the winter in non tropical climates.
So the most natural metabolic states would be either zero ketosis as our ancestors in tropical climates likely lived, or sporadic ketosis as our ancestors in every other climate in the world likely lived.
However it is unlikely that any significant amount of our ancestors lived in ketosis at all times for many years at a time or their whole lives.
Therefore, should we limit time in ketosis to the most realistic assumption about our ancestors which would be all winter and stay in for a maximum of three months or so?