Individuals on carnivore or ketogenic diets do not have pathologic insulin resistance and their muscles will accept glucose within days of reintroducing carbohydrates.

“I think you're right in the short run ketogenic diets in a non-trivial subset of people generate profound insulin resistance in the muscle again I don't even know what insulin resistant means if we're gonna be truthful like if we're gonna put me in the confession booth I don't have a goddamn clue what that term even means it's so ubiquitous does it mean the failure of one type of cell but not another type of cell to respond to insulin signaling I mean all of these things but I think I know what you mean you couldn't see huge elevations in glucose and insulin and basically a complete refusal of the muscle to accept glucose in someone on a ketogenic diet when they first encounter a carbohydrate but I think it's generally also regarded that after about three days of carbohydrate refeeding that effect goes away and that that effect is sort of a physiologic response to an individual who's been so carbohydrate deprived that their muscles are basically saying any glucose in the system we're going to preferentially save for the brain since we now have all the fatty acids and beta-hydroxybutyrate in the world we need as metabolic substrate”