I would not consider Muslim or Jewish fasting a good example. Both Jews (on "Yom Kippur", Day of Atonement), and Muslims (On Ramadan) do a "dry fast", that is

I would not consider Muslim or Jewish fasting a good example. Both Jews (on "Yom Kippur", Day of Atonement), and Muslims (On Ramadan) do a "dry fast", that is - without any liquids either. That fast CANNOT be sustained for long, and becomes dangerous after just a couple of days regardless of your fat/energy reserves. Jews do it for 25 hours once a year, and traditionally eat an extra lunch upfront ("Mafseket" - "The pause meal") and a regular-to-larger dinner afterwards. Muslims do it for a month, but only during daytime - and feast all night (some who can afford to, just sleep all day and stay up all night and don't actually fast). Neither of these traditions are healthy in any way. I'm not as familiar with the Hindus and Jain fasting traditions - but I know some of them last months and all of them involve water drinking, so those are likely indeed healthy.