This is going to be a rather short post, and I'm not going to reference it. I simply don't have time. (As always, feel free to contest any claims you feel are erroneous in the comments.) But something has been bothering me for a long time about the whole nutritional ketosis thing, or what I call NuttyK, and I just couldn't put my finger on it. And then it hit me, as I was looking into the buffalo hunting thing ...
Humans likely do have a long history of being in ketosis for periods of time. Ketosis ... as in the metabolic adaptation to starvation to preserve lean mass and reduce glucose consumption by the brain by providing a fat-derived alternative fuel. These humans were in prolonged periods of caloric deficit without a "need" to be ... in other words they weren't overweight dieters getting most of their energy from surplus stores. They were in starvation ketosis.
Humans around the globe have historically subsisted on the foods available to them. It is rather interesting when you think about it, how different these diets can be for groups of humans who have settled even in very close proximity to one another. While trade may not have always had a positive impact on the health of various populations, humans seem to be an eager bunch to do so, rather than to starve or even settle for monotony. There is little allegiance to dietary purity in the face of starvation -- except for a few religious martyr types -- throughout the course of human history.
The plant v. animal subsistence seems to be largely (but not entirely) dictated by climate, with popuations at higher latitudes consuming more animal foods with a shorter to non-existent "growing season" for edible plants. There are also various patterns based on terrain and such. While there are apparently no strictly vegan populations, there are some nearly-vegetarian ones, and while there are some populations that are nearly, if not entirely, carnivorous seasonally, there exists none purely animal-consuming either. In some regions, the scarcity is water, in others it is food. While Jared Diamond claims agriculture is the biggest mistake in human history, his ideas are premised with some misplaced idea that hunter gatherers were a leisurely bunch, picking and choosing from year round abundance of preferred dietary staples. Not so.
Sticking to North America, native tribes, especially in the north, suffered periodic if not seasonal stints in starvation. STARVATION ketosis.
These would have been alternated with periods of being replete with nutrients, perhaps the occasional feast, but almost invariably including sufficient carbohydrate and calories so as to be nowhere near ketosis.
Most of these tribes expended a great deal of effort in preserving foods for the impending famine. One might even say it was an obsession. Preserved foods included animal fat tissue, which for the land mammal hunting tribes was NOT a year round abundance, or even a guaranteed seasonal abundance. Why would anyone presume that other animals were somehow exempt from seasonal famine and hardships (doughts, floods, heat/cold waves, etc.) that humans endured?
Pretty much EVERYWHERE in the literature you see references to starvation = presumed ketosis. And in periods of abundance (not late winter-early spring) you had carbs = no ketosis. Pretty much NOWHERE do you find examples of nutritional ketosis.
Nutritional Ketosis is an oxymoron and NOT part of the natural human condition.