I think the importance of food should be emphasized this way:
1. remove the ability to heal by waiting, or even sleeping. Instead, food serves as a method to slowly generate a large amount of health over time. You can even eat and then wait, and then your health will be full. Potions on the other hand should have quick instant effect to aim in battle.
2. to make food more important as a health regen agent, make health potions more rare, and restore health spell shouldn't be available to everybody upon beginning of the game.
3. dishes can be made using ingredients that have no negative effects. For example, make food items such as apple, pear, cheese, graqes, wheat, meat... only have positive effects. You'll need at least two of these kind of ingredients to make a dish.
4. to poison a dish, you can add ingredients that have certain negative effects that will damage the health such as damage health, fire damage, frost damage, poison damage etc. or even paralyzation!
5. food should have containers. Remember those useless plates and bowls? when you cook you require one of them, and it becomes part of your dish. after you eat the dish, you get the plate back.
6. By St Frantic: food can be used as a substitute for alchemy. This gives us a variety of possibilities:
A. For characters not specializing in alchemy, they can use cooking to make rudimentary potions;
B. Make it that potions can only be made in town in sophisticated alchemy labs. while you are on the run in the wilderness without access to the lab, you can use cooking to make dishes that serve as a substitute for potions.
How do you think?