> ancient rome and medieval europe are really different
Why? Of course Northern European had different diets (e.g. lard instead of olive oil etc.) but on the Mediterranean cost diets weren't that similar.
> you can enter ketosis every day on a diet of carbohydrates by eating one or two times a day
So being on the brink of starvation all the time? Does not seem sustainable.
> all of this could have applied to most people until relatively recently
Highly unlikely. What makes you think that was the case?