High-fat/low-carb 'is' natural.  Look at the traditional diets of the Inuit ( fat from seal and caribou );
Plains Indian ( buffalo and deer fat made into pemmican* ) and West Coast Indians ( candle fish grease );
Masai ( Cow fat and cow blood ), and many other traditional cultures.
That is why it is called things like the Paleolithic/Caveman/Hunter-gatherer diet.      

* Like the Inuit(Eskimo) they gave most of the meat to their dogs, but dried some of it.  

Fat is where it is at.  We are not what we eat anymore than cars are made out of gasoline.