Strictly applied, I've followed a "ketogenic" diet by definition. My body operated on ketones for prolonged periods over about a year.
This came from intermittent fasting. This did not come from a strong meat-based diet with high fat. I believe those are very bad ideas.
The process was roughly Mon to Wed/Thu/Fri with no food whatsoever. I used keto-sticks to ensure my body switched to ketones as fuel.
Each day I stepped on the scale, I lost 2/3 - 1 whole KG a day. It was amazing.
Psychologically, there was a sort of buzz that I felt enhanced focus and was pleasurable. I was also amused at how I conquered hunger. It stopped ruling my life and I decided when to each and how much.
Physically, I did not feel like I could climb a mountain or anything. I felt light and floaty, but also slow and somewhat weak. This was not necessarily a bad thing at all. I did _not_ feel heavy and sluggish or lethargic, but rather capable of focus and walking around, just perhaps slower, but more comfortable.
Heads up: the first 3-day session was very hard. Headaches were an issue. From there it became easier. Then second nature.
I lost 20+ kilos over the year, but most of that was during the 3+ day fasts. I took many weeks off throughout the year and easily switched from normal eating to fasting throughout.
I have also tried meat/fat based keto diets and I think they are bad. They did not work for me in any way, and I have red of people damaging themselves from this harmful diet fad. I tried many other diets as well, but fasting was all that worked.
Some of the weight was regained, but I still fit into the clothes I bought at the target weight I reached through this method. I happen to believe this diet is perfectly natural and even medically beneficial.