In order to stay balanced and healthy, and to give your body the multiple nutrients it needs to run well, I recommend having a combination of 2-3 food groups in each meal. I recommend three small meals a day.
It's easy. A fish sandwich is a good example. Two slices of bread (2 from the carbohydrate group), a serving of cooked fish (1 protein group), with lettuce and tomato (vegetable group). (Avoid a lot of tartar sauce or mayonnaise, only have a teeny, tiny bit if at all.)
Or a bowl of cereal with fruit, which contains carbohydrates, dairy (milk), and perhaps some fruit (like sliced bananas, strawberries, or blueberries -- yum!).
A salad is terrific. Try a spinach salad (vegetables), with hard-boiled egg (protein), red peppers (vegetables), and some shredded cheese (dairy) and croutons (carbohydrate). Fantastic. Go ahead and have a tablespoon of salad dressing -- the regular kind, not the awful, poisonous "low fat" chemical kind.