I just posted about this not too long ago! I have AS and attempted a 48 hour dry fast and felt more pain initially during the fast but the night after my refeed felt much much better. Maybe even better than before I started the dry fast. I focused on repopulating my gut with healthy flora since a lot of auto immune can be linked to gut issues. First day of my refeed I drank baking soda and water for first hour. Then drank mineral water for the next few hours and took a shot of a non diary coconut water kefir. (Diary might negatively affect AS). Then moved on to sauerkraut at night then bike broth after. Also had some coconut water. I heard the refeed can be just as important as the fast itself. I plan on doing a 5 day soon!
So for dry fasting, days 1-3 are cleaning up senescent cells you also have slight stem cell activation but after day 3 stem cells EVERYWHERE turn on, but the stem cells need 4 days to properly divide and proliferate, hence the need for 1 week for maximum benefit.
You really need to read this book.
https://www.amazon.com/Phoenix-Protocol-Fasting-Healing-Extension/dp/B085DRTWBW
You sould also work your way up to a week if your body isnt ready, like fitness you shouldnt jump into squatting 100kg, same with fasting.
I’d also highly recommend you look into carnivore diet, it’s not the best super long term but it is by far the best diet for auto immune. If you want we can do a google call and talk more, i’m not a dr, just someone who has been into fasting, diet, nutrition, biology, and fitness for years. I can point you to some good resources. Respond here or DM me.