This has been my experience:
1-3 days fasting - re-feed any way you want (before I was keto I ate a half a pizza at the end of a 3 day fast, no issues)
5-8 days- eat a small meal of “normal” foods (for me it’s boiled eggs, some bacon, a few nuts, a little bit of butter, olive oil). Make a plate, eat the food and then go do something to take your mind off food. Do not eat from a container/stay in the kitchen, it can easily lead to gorging (this rule works for any fasting over 5 days).
8+ days- same rule as above but add in some kraut or maybe a fermented pickle to the small meal.
- You’ll fill up fast (amazingly so) so take it slow and stop at about 80% “full”, give yourself several hours to digest.
- Bowel movements may be loose, that’s been very normal in my case. Make sure to get lots of sodium on your re-feed day as too little will result in constipation in the days after a fast, it can get tough if you don’t really hammer the sodium!
- Don’t be surprised if you get tired after eating. The body has had lots of “extra” energy to put to use while you’ve been fasting, when you eat you have to “divert” some of that energy to digestion, often resulting in a crash (for me, kind of like a post-sugar crash).
Don’t overthink it and don’t believe the BS about having to break-fast with fruit only or fruit juice or whatever, just don’t go crazy eating some new food you’ve never had before and it should be fine.