A very low carb diet has been used for epileptic children for about 100 years. It helped them have less seizures. I think based on what I have personally read from these studies though, there are *some* problems for the diet, at least potentially for some children. There were the typical side effects: stomach upsets, headaches, higher LDL cholesterol readings, but there were things like development of kidney stones in children as young as 4, quite a few did develop heart problems, there was for some a sudden decline in selenium with long term adherence to the diet, even while eating foods rich in it (this led to some of them actually having heart attacks and recent study started in 2014 had this loss of selenium happen to a few adults with one other know condition, MS, diabetes, etc), however, coming off the diet for a few weeks appears to correct this issue. Long term adherence was classified as four years or more, so I DO think that is something people on this diet should have checked in on with their regular bloodwork. About the worst thing though is quite a few children stopped growing and some teenagers did not hit puberty. What that means for adults, I do not know. For quite awhile, researchers thought it was the drugs being used, but then found some children who were taken off or had never been on the drugs to start with still developed these concerns. Over the last 100 years, there have been lots of modifications made to this diet to help prevent some of this, without much success. As a side note, I would like to say there is a reason parents of epileptic children have moved towards treatments like canabis oil.
Lets be clear: I do a low carb diet myself to control my condition, though I do not go low enough to put myself into a ketogenic state. This is just information I found on the diet in the longest studied people who have been on it. Personally, I have other concerns that I think do not make me a good candidate to be on this diet in the strictest sense, though I have recommended it to others, while mentioning the possible side effects. I 100% believe that the diets set out by most diabetic associations, educators and doctors is terribly flawed and one that keeps a lot of us on medication when we do not *always* need to be. I believe lowering your carb intake reduces inflammation and allows you to be a healthier version of yourself. For myself, these days I take in 75-100 carbs a day, have normal blood sugar values (4s and 5s at fasting and post meals), seldom feel hungry, am a proper weight and have gain muscle definition that I otherwise didn't have. I feel the best I have ever in my life.
I am just not sure that long-term adherence to Keto without breaks is the best way to go, but I DO acknowledge that there are people who feel it is right for them. I think it is most important of all to listen to YOUR body.