I don't think there is a set amount anyone should eat, I just eat when I'm hungry and keep it under 20 carbs. If you are taking a good multivitamin you shouldn't have to worry about in-adequate nutrition. Also drink plenty of water. For work I'd bring a salad or something in a tupperware container, and also some ham/cheese rollups to snack on in case I got hungry again. Just remember that you don't have to eat them just because they are there (that's where I always had trouble with sack lunches).