Eating and drinking are very important...
If you let yourself starve or dehydrate, your mental state will be affected,
and you may have problems performing even the simplest of tasks.
Typing affected will give you an indication of your current mental state.
Sitting, resting and sleeping will increasingly contribute to better your
mental state (if done while not starving/dehydrating).
You will die from starvation and thirst.
Being hurt badly in battle ("That really did HURT", and "You wish that your
wounds would stop BLEEDING so much!") as well as poisoning will also have a
rapid negative affect on your mental state.
If you eat a food that has spoiled, you will feel sick, which also hurts your
stamina. While it is possible to over-eat and to drink too much liquid,
doing these things will not hurt you, only waste the food and water used to
accomplish them. The game will send you the echoes "You are stuffed" and "You
feel bloated" when eating and drinking any more, respectively, would be
futile.