Here we go again. Long term keto? What does anyone think our paleolithic/Pleistocene ancestors ate for 2 1/2 million years? Here’s an article I posted a week ago at Breakfast with Bubba:
The article is a rebuttal of claims that for the better part of 3/4 of a million years our Pleistocene ancestors ate roasted tubers and became fully human as a result of the increased digestible carbs. Because the human brain needs lots of glucose, doncha know. Apparently, the author of this nonsensical hypothesis actually used potatoes as an example. Potatoes! I suppose she went to her local supermarket and bought a bag of Idaho Russets, thinking they were typical spuds our ancestors would have eaten. Roasting them on a stick around the campfire.
The author of the linked rebuttal discusses a lot of problems with the claim, among which is the most obvious. Wild potatoes are native to South America (Peru and Bolivia mostly) and our Pleistocene ancestors could not possibly have eaten them 3/4 million years ago or even 20K years ago, roasted or otherwise. So any nutritional facts and/or suppositions based on potatoes is totally irrelevant to the evolution of human beings during the Pleistocene. By the way, Amber O’hearn addresses this same issue here.
I bring this up simply to point out a fallacy that many appear to share. That is the fallacy that Pleistocene flora was pretty much similar to Holocene flora. In other words, our ancestors didn’t have the convenience of a local market like we do. But, they could just wander through the local orchard or meadow and bring home the same luscious fruits and veggies. Well, no they couldn’t! The luscious fruits and veggies we know today did not exist.
Our ancestors ate mostly fat and meat, in that order. Aside from a very few seasonal items like nuts and berries, plants were mostly indigestible cellulose and totally inedible. Try a salad of Kentucky Blue Grass to find out what that means. 
Our ancestors were in ketosis most of their lives, with possible short excursions when some particular berry or nut was in season, or someone found a honey tree. No scientific research on long term keto? I think there’s about 2 1/2 million years of it. On the other hand, the recent (7-8K years) carb-centric diet doesn’t seem to be working out very well.