Holy shit, Angus Barbieri fasted for 392 days! Went from 207 kg down to 82 kg. Five years later he was 89 kg, so he kept it off.
Maybe I should go beyond 40 hours? I'm not hungry. I've got electrolytes.
Discussion
Go for it. I lost maybe 12kg after 3 weeks. Once you make it to day 5 you don't think about food anymore. Just look out for low blood pressure and potentially passing out when standing up. If you don't have fat to lose, you will start consuming muscle, heart muscle being the worry.
The benefit of multi-day fasting versus multiple days of fasts interspersed among days of eating isn't clear to me. There might be some genetic pathways that only get turned on once a fast gets long enough. But there also might be some malnutrition that is harmful (a lack of certain substances that are better if they were around, like vitamins, antioxidants, etc). We know the latter is true of electrolytes, so it may well be true of other things.
So in comparing fast-fast-eat vs. fast-eat-fast, I decided to eat yesterday and fast again today.