Why Do Fats Contain More Energy Than Carbohydrates?

The amount of calories a type of food has depends on the number of carbon atoms in a molecule of that type of food.  When your body burns "energy," it is actually turning the food source into carbon dioxide (which you eventually breathe out).  Thus, the more carbon a molecule of food has, the more energy or calories that food contains.  While both carbohydrate molecules and fat molecules contain carbon, carbohydrate molecules also contain many more oxygen and hydrogen atoms than fat molecules.  So, one gram of carbohydrate contain fewer carbon atoms and more other types of atoms than one gram of fat, which is almost all carbon.

Fats do take longer to burn because they are a more complex polymere. Sugar is a simple compound which is easy to break down and prime for quick energy. It's all chemistry.

Fats contain more calories which equates to energy because it burns more slowly where as carbs which are sugars burn quicker ,the body uses up sugar fast,fats takes longer