You have to be careful not to become obsessed about your diet. Some simple adjustments can make a big difference and the exercise you are doing is the major factor when done consistently , in terms of fitness, weight and health. The first thing to do is to cut out the "rubbish" . If you have to snack then eat good things, fruit nuts/dried food etc. Don't use energy bars as snacks either. They are fine for races and post training recovery but not a substitute for eating well. Pasta is good, whole-wheat rice/pasta/bread is better. Breakfast is important - porridge is great as there is a slow release of energy which will help you feel less hungry. Lunch / dinner could be things like baked potato but not loaded with butter/maybe with tuna/baked beans etc lentils another good option. Also lean meat/chicken/tofu and oily fish. A banana half an hour before training is good, but some people cannot do this. It can be a matter of trial and error but definitely don't change anything on race day.