Hi I train four or five times a week, three of which are with a trainer. I work out in the morning so I have been advised to eat about an hour to an hour and a half before my work out. Porridge/oatmeal is brilliant. Sprinkle with a few flaked almonds or sunflower seeds and a drop of honey , [if you like it sweet].
If you work out in the afternoon or evening a wholemeal pitta bread with lettuce, hummus or chicken would be good too.
You need energy foods that are low GI. This means that they release energy slowly and give you the stamina to continue a vigorous workout. You need the sustenance to keep going. Keep well hydrated throughout your work out and when you finish you can have a banana or boiled egg or something with protein.
Protein keeps you slim. Some form of carbs are needed to help you when you work out.
Hope that helps.x