Okay. There IS no fixed amount, because it depends on diet, on your previous metabolism, what you're eating, when you sleep, and so on. The basic rule - if you're doing slow activity during your 'awake' time, then you slow your metabolism.
As for food. Eat slow, complicated carbohydrates, because they are slow releasing into the blood, giving you a longer supply of energy for less food. Pasta, potatoes, porridge - all of these are good. Starch carbohydrates as opposed to sugary ones. The break-down takes longer, so normally you stay away from them, but if you're only eating one meal a day, and it's fairly late, you'd be better off with carbohydrates rather than protein, like meat and eggs.