This isnt a matter of believe. There are lots of prisoners who went on hunger strikes and perished from it. With them starting with a background of a normal western diet.

https://en.wikipedia.org/wiki/1981_Irish_hunger_strike 45-73 days till death with most lasting 60 days.

Holger Meins lasted 58 days despite forced feeding. https://de.wikipedia.org/wiki/Holger_Meins

List is obviously a lot longer but they offer a great dataset