Every day, your character will automatically eat whatever nourishing food he or she has in inventory, unless a sufficient amount of nourishing food was previously consumed using the eat button. You always eat the food that's the heaviest, unless it's a dual action food in which case the single action foods are consumed first. If your character has no food, he or she will begin to starve. After twenty days without food, your character will die.
Order of Auto-eating
Less efficient foods, which weigh more per meal, are eaten before the lighter more efficient ones, and that nutritional foods with no healing capabilities are eaten before those which can also be used for healing.