I’ve heard the argument that those who go off keto have more insulin resistance or ‘impaired glucose tolerance’ thus it is “dangerous.” Technically this is true, but it’s not dangerous. Unlike the disease of insulin resistance, which takes a lot of time and effort to reverse, this phenomenon, often called the ‘glucose sparing effect,’ is temporary and adaptive.
Given the lower amount of glucose in a keto diet, the cells in our bodies that don’t need glucose become more resistant to the glucose we do have so it can be spared for the few cells that do still use it. It also acts as a muscle-sparing effect by reducing the protein needed for gluconeogenesis.
Here’s a reference addressing the “hypothesis that the restriction of carbohydrates, substituted by the high consumption of fats, induces a state of glucose intolerance and insulin resistance in rats”
https://www.physiology.org/doi/full/10.1152/ajpendo.00580.2013
After explaining why and how this happens, they suggest - “For that reason, it should be common in clinical practice that patients submitted to oral glucose tolerance tests not be under severe carbohydrate restriction, since this could alter the response to the glucose overload. Thus, we suggest that the results from Bielohuby et al. (1) can be interpreted as a unique and not necessarily harmful metabolic condition, which is characteristic of this state, besides being transitory. As demonstrated by Kinzig et al. (4), the glucose intolerance and the peripheral insulin resistance are rapidly reversible with the reintroduction of carbohydrates in the diet. Additionally, the condition of induced insulin resistance is different from that induced by mitochondrial dysfunction, caused by oxidative stress generated by the glucose overload (3), which evidently does not occur with the carbohydrate restriction. In that context, ketogenic diets have not yet demonstrated adverse effects in the mitochondrial function.”