>>76729429
A calorie is defined as the potential energy in a given food, as measured by a bomb calorimeter.
A bomb calorimeter is used to measure potential energy by dehydrating food, grinding it into a powder, and burning it, then measuring a change in temperature in the device.
The human body obviously does not process energy in this manner.
Depending on a variety of factors in relation to the food (density, fibre content, macronutrient type etc), the body will expend a certain amount of calories processing the food for it's potential energy. Macronutrients such as fats have a very low "processing overhead", while proteins are relatively higher. This is known as the thermic effect of food, and is well researched and documented.
Obviously this shows that CICO is a flawed approximation.
If you take two identical individuals who have a TDEE of 2500 calories as estimated by CICO models, and feed one 2500 calories of butter per day, and the other 2500 calories of chicken breast, the chicken individual will lose weight, while the butter person will gain it.