Your best bet is to learn about the types of fuel the body can use and how it does so. That will let you decide on what would be your preferred diet (i.e. there's no point in me saying "just eat meat, veg and some fruit and nuts. Nothing processed like potatoes or grains" if you know that carbs are ideal for your lifestyle).
Keep a food diary for a few weeks and write down everything (everything!) you consume over that time and you also might notice a pattern emerging too.