Combustion of Proteins, Fats and Carbs:
Generally speaking, proteins, fats and carbohydrates provide different rates of combustion. Fat is one of the most efficient, compact sources of energy in all the foods you eat. One gram of fat when burned in the body will yield 9 calories. Proteins and carbohydrates are not as efficient. The rate of combustion for both of these fuel sources is 4 calories per gram. Thus we have a 9-4-4 ratio of values applied to the main elements of a menu.