The food priamid along with calories in, calories out really does work.
I heard an explaination one time about todays obesity problem that makes sense. A loaf of store bought bread used to mold in 3 days now days it stay "fresh" for two weeks. Children used to eat homemade cookies and drink soda made with real sugar and not get fat.
A homemade choc chip cookie stored in a ziplock baggie gets stale in less then one week. Stored the same way a "Chips Ahoy" cookie will be edible for much longer.
Now days many of the store bought foods are processed, refined and full of preservatives. Our bodies are not made to break down these types of foods so it gets stored.
Not sure if it's all scientificly true but it make sense.