Obviously people can eat as they please. I don't follow any one diet. One comment about keto is that keto itself is not ideal but the act of going in and out of it. Hence 18 hour fasts are considered very beneficial and will pretty much protect you from obesity and diabetes.
I tend to fast anything between 12 and 16 hours a day (including time spent asleep)
Beyond I try to go for a healthy balanced mixed diet. I eat carbs but mostly brown bread, pasta etc. I keep my processed and junk food to a minimum, replaced sugar with xylitol while avoiding sweet treats as much as possible. I also try not to eat massive portions as much as possible
It seems to work for me. All my blood tests come back clear, low glucose levels, no heart or blood pressure problems and apart from a slowly creeping belly that comes with age I am a healthy weight and nowhere near obese.
I do have cheat days. We're here to live after all and I don't see any harm in one take away binge a week.