While I don't think a ketogenic diet is an optimal diet in terms of longevity or overall health (as all blue-zone diets are carb rich), it does appear to confer some benefits in the short term which are fairly compelling. The vast majority of humans are adapted to seasonal eating, with high carbohydrate diets during spring, summer and fall, and very low carbohydrate diets during winter (or during the wet/dry seasons). I suspect that our bodies have evolved around short periods of keto-adaptation as part of a natural rejuvenation cycle. Given our modern non-seasonal eating habits, that would mean we're missing out on a natural bodily process that is important to health.