Here is an interview where Dr Nadir Ali recommends doing 18 hour fasts three days a week. I basically do them 7 days a week although the number of hours might vary from 14-20 depending on what time we end up eating.

Wide range of topics including not losing muscle. Shows science behind his recommendations.

See the next video linked in my reply below where he changes his mind on longer term fasting.

https://www.youtube.com/watch?v=6yprtVjBKic

John

Edit: As a reference for the above video. I do not have an insulin test for when I was taking 100 units of exogenous insulin. But I did take one after being on a low carb diet for 6-7 months. My fasting insulin was 7.6 with a reference range on my test results of 2.6-24.9. I have watched other video's of other doctors that say a healthy person should for sure be in single digits. So my results of being diabetic taking 100 units of insulin, going on a low carb/keto diet, dropped my insulin levels into good range and my blood sugar controlled better than when I was taking insulin. Low carb worked to reverse my type II diabetes. Had I eaten better for the many years prior, I probably would have never become diabetic.