Just a simple point really.
a bowl of my porridge with milk is about 600 calories, a low fat yoghurt is about 150 calories.
One fills me up till 2pm, the other I'm hungry by the time I get to work.
Dont look at low calorie as a great thing, don't get me wrong, there are great low calorie foods. Foods that are high in calorie are not necessarily bad for you if they are nutrient dense, they will actually fill you up for longer and in fact, make you eat less.
And one more thing, fat is incredibly good and important for your brain especially, low fat = high sugar in most cases, better to choose fat over sugar, unless your doing high intensity.