In 1965, 27-year-old Angus really did fast for one year and 17 days. He ate no food at all, and lost 125 kilograms (19.7 stone).
Angus was reportedly sick of being obese, and checked into the University Department of Medicine at the Royal Infirmary of Dundee weighing 207kg (32.5 stone). He told hospital staff he was ready to cut out food together, so doctors happily agreed to monitor his progress.
Angus’s doctors didn’t really expect the fast to last long. But they thought a short fast would help him to lose some weight. To compensate for his lack of nutrients, he was prescribed multivitamins to take regularly, including potassium and sodium, as well as yeast.
It all depends really the important thing is why you want to fast is it because of weight or a medical condition after that the length in my opinion to start with should not be more than 7 days once you understand the fasting process you can try longer
I plan on switching from prolonged fasting to alternate-day fasting once I reach the 20% body fat marker. I can’t remember which studies I read at the time, since it’s been years, but there was something about fasting-adapted animals like penguins even begin to consume more lean tissue after falling below 20%. Think there was an old Russian study where they starved dogs to death too that demonstrated the same 20% body fat threshold. Lost the specific details over time, but the notion of 20% stayed with me throughout the years.