Wikipedia says the ketogenic diet can help reduce seizures in some children with epillepsy, but it says the benefits don't always go away after discontinuing the diet (I'm paraphrasing). I hadn't heard that before:
"Around half of children and young people with epilepsy who have tried some form of this diet saw the number of seizures drop by at least half, and the effect persists after discontinuing the diet."
https://en.wikipedia.org/wiki/Ketogenic_dietepilepsy_ketogenic_diet_