Answer is: much energy can be gained by breaking the bonds between atoms in the fats.
Fat, carbohydrate and protein are the three main macronutrients.
Fat molecules contain chemical energy and they are composed of triglycerides.
Fat is the most energy dense, the most efficient form of energy storage and do not bind water thus do not increase animal body mass.
For example. fat burning in human organism release energy that we use for walking, learning, etc.
