Source?
> Ketosis is the default energy System, in that all things being equal when a person doesn’t introduce any food they naturally go into ketosis. People literally need to eat certain foods that spike insulin to get “kicked out” of ketosis.
That is not a sound argument for it being the "default energy system". It makes much more sense that "default energy system" is that which directly provides the energy source REQUIRED by the brain[1]. Additionally, our closest ancestors (primates) were frugavorian omnivores. Ketosis is a state of starvation and the long term complications from it support that[2] but I guess starvation could be argued to be the "default state" of all living things.
1. https://www.ncbi.nlm.nih.gov/books/NBK28048/
2. https://www.thepaleomom.com/adverse-reactions-to-ketogenic-d...