People on a Ketogenic diet report need only 6 hours of sleep with no adverse effects. I am on Keto plus I also meditate, and I currently sleep 4-5 hours a night, but I'm feeling awake and refreshed. This is both awesome as I used to be an owl, and it freaks me the hell out. This is completely unreal, and I wonder if its going to last or if it is just the usual temporary keto insomnia due to disrupted melatonin synthesis. It needs glucose and takes a while to adapt (Glucose -> L-Tryptophan -> Serotonin -> Melatonin).
Anecdotally, I experience the same thing when I'm on keto. I have much more energy during the day and I'm not groggy in the morning. Otherwise, it's nearly impossible for me to wake up even if I've had 8+ hours of sleep, and I often sleep through my alarm.
I'm more of a low carb person rather than keto, but I can anecdotally confirm that how many carbs and/or sugar I have the day before does impact my alertness the next day regardless of sleep.
I also do time restricted feeding and skip breakfast. If I load up on carbs (particularly crappy ones) the day before, I feel hunger much more the next morning than if I ate clean during my feeding window.
