what is the difference between caloric fuel value and physiological fuel value?

plz dont give the definitions, i have read them in my boo, bt i dont undrstand.. explain in ur own simple words what the diff is.

Calorific value of a substance tells us the total amount of heat energy released after combustion of said amount that substance (fuel) say 1 Kg. This amount of heat released is particular or constant for a substance. It is expressed in terms of kilo joules per Kg (KJ/Kg).

The measurement of amount of energy available to the body after burning of a fuel (food) is termed as physiological fuel value. This is because body does not completely absorb and metabolize ingested nutrients. The energy lost in excreta, respiration etc.  must be subtracted from  total energy value (Calorific value) of the food to obtain amount of energy available to body (physiological fuel value) from consumption of the food.

Hope this helps!!