OK, so, put up or shut up. Go without food AND water for just 3 days, and let us know how you feel.
I second ikka's suggestion.
Don't worry, you won't die--Orthodox monastics in good health, and a fair number of our more vigorous and pious laity and clergy go without food and water for the first three days of Great Lent every year.
I've never been able to do the 'without water' part for more than a day without getting severe headaches.
BTW, the without food part gets easier after the middle of the second day, still. . .try it before you post again.
Experential knowledge trumps theoretical knowledge.