Another factor is fats really like 'low calorie' food options where the dietary fats have been replaced with indigestible hydrogenated oils so they can eat more volume.  Problem is, a) you need dietary fat and will crave fatty foods if you don't get them, and b) they leave the carbs and simple sugars because those are lower density even if they are more readily converted to body fat. Then a carb crusher comes along and eats 5 New!* Low Fat Formula! toaster strudels, but still wants toast with butter.  Now they've had 1200 calories of sugar, 150 calories of fat and 800 calories of carbohydrate, and they still want a glass of milk.