I know one person on it for psychiatric/neurological reasons who's likely to stay on it very long term.   Regressive autism with regular grand mal fits starting at age 7. His mother is a doctor and tried everything. The keto diet helped a lot with the fits but not much with the autism. She tried something else - I forget what - which did make a difference (I haven't seen him since before). Meanwhile the kid is on a very complicated dietary regimen he doesn't have a prayer of ever understanding.