The amount of heat liberated from the complete combustion of 1 gram of food in a bomb calorimeter (a closed metal chamber filled with O2) is its gross calorific value or gross energy value (G.C.V).
The actual amount of energy liberated in the human body due to the combustion of 1 gram of food is the physiologic value (P.V) of food.
It is measured in K.cal/gram.
| Food Substance | G.C.V (in K.cal/gram) | P.V (in K.cal/gram) |
| Fat | 9.45 | 9.0 |
| Protein | 5.65 | 4.0 |
| Carbohydrate | 4.1 | 4.0 |