[bitL]

You should have tried the 4th day, usually the first 3 days are the worst, then the body completely switches to burning fat and learns how to do it efficiently. 6th day is for me usually the worst sudden crisis, then from 7th to 21st day I have absolute mental clarity, I can finish very demanding mental projects quickly and require only around 4 hours of sleep, then up to 30th I feel normal and slowly start to get hungry. After the fast I feel like after a great sauna session, but it lasts around a week. It feels like having a superpower. However, physical exercise ability goes away very quickly (I actually measured it every day and even went mountain-biking to steep hills to see how much my performance degrades and it was downhill literally and figuratively).

[labawi]

YMMV, but yes, with full supplies it usually takes about 3 days to deplete sugars and switch to fat.

If you're not used to keto, switching may be physiologically hard. Gradually transitioning from carbs to fat, and then or later to fasting may be easier on the body, though a prolonged hardship for the mind.

Once you get used to it, switching is a normal thing to do, though again YMMV.