Well, the human body can go long periods of time without food and still survive (decreased quality of life), but not nearly as long without water. After a long enough period, the body literally starts eating itself to obtain the energy that it needs to function. Vitamins and minerals are important, but so are carbohydrates and proteins. Silkiechicken could speak more about this, as could any other medical/biological people here.
I wish you the best in your endeavor.
What are you a nurse of, if you don't mind me asking.