If you have free time and want to shred, boxer cut is king. Dry fast, hard exercise until you simply can’t take it anymore. Then have a soak in a cool bath or pool and decide if you can do another round. Keep going until you have to refeed and rest a while, then do it again. Those who know their bodies can absolutely shred 10+lb a day like this and not lose a lot of lean mass. Obviously, not sustainable as a lifestyle, but this is really just “ripped for the beach,” sort of method you would do once a year or so. And at that amount it is probably safe.
As far as normal-er fasting goes: I’ve recorded a few outlier fasts for weight in the years I kept record. The first 5-day fast I did I lost almost 3.75lb per day and I attributed that to being very sick. I had a particularly hard case of strep which didn’t actually heal until the fifth day. My guess is that my extremely hard working immune system was burning a lot of extra energy in that fast. My normal fast of 3-5 days sees me lose only 2lb per day so I nearly doubled that just by being sick.
The other quirky fast where I lost an oddly high amount per day was 3.5lb per day while I was fasting at a different location than usual. I was higher altitude, though not by much, just a few hundred feet higher elevation. I was mildly ill to begin that fast but recovered on the first day so I am not sure that was relevant. Interestingly in this case: I lost more weight per day as time went on. This is completely atypical for me as I usually record a slight increase and then slight decrease in a bell curve sort of pattern. I imagine if this fast has been longer (it was only four days since I had other things to do) I could have come up to an average even higher! Very weird but interesting.
tldr: According to my fasting journal of a few years the high points of my weight loss were being sick and being higher altitude. But if you just want to shred, do the boxer thing.
Dry fasting + Warm (Hot but not fully hot) Yoga + a little walking. Down 5 pounds each day and it all stayed off after refeeding. I was only able to keep it up for three days though before getting exhausted.
Wouldn’t recommend to be honest. I felt so shitty on day three that it was way more mentally challenging for me to get into my next dry fast. I took months off.