Hello,

Energy released on Complete combustion of one gram of food is called Gross Calorific Value.

Gross calorific value of proteins - 5.65 kcal/g

The actual amount of energy liberated in the body from carbohydrates, proteins and fats is called Physiologic value of food .

Physiologic value of proteins - 4 kcal/g

Gross Calorific Value is Measured using Bombs Calorimeter or other lab equipments where as  Physiological Value is the actual  amount of energy liberated.

Since Gross Calorific Value is measured using equipments, the value given by it is slightly higher than the physiological value which is exact .

Hope this was helpful