posted by Lena .
Why is the experimental Cal/g value usually less than the Cal/g value calculated from the Information on the nutrition label?
The calories/gram on the label is a complicated ESTIMATION, based on the age of the person eating (babies vs adults have a wide range of combustion efficiency in cells), and the amount of calories lost in human excretion due to proteins, sugars, and carbohydrates present in the feces and urine. Frankly, the number of the nutrition label are just not accurate due to the variance in humans consuming the food.
There is not short answer to your question, other to say that the bomb calorimeter and the body processes have different heat conversions, and in the body, there are losses in the digestion and metabolic products.