[mister_mister]

They are unit of energy and that is correct. But they are not the unit of energy that cells use, they use ATP that is created from ketones, fatty-acids, glucose and oxygen[0]

Measuring food through calories, which are derived from burning food is therefor quite old technology, it's from 1800 when steam engines where main way of powering the western world.

As a thought example to push CICO model to it's end: For example we can't eat coal, but it's very calorie dense. According to CICO model we should be able to eat just little bit of coal, and drink tiny amount of fuel. So that would also suggest there is more to the story of nutrition then CICO.

Mammals are not as simple as factory machines.

For example CICO would suggest to lose weight to eat 500 calories less then normal, as average that would be 2500 for men. But if we would rephrase that: In order to lose weight eat 1/5 less then normal. Then that would have the same effect, that is issue with calories they tell a story about food but it's not the full story. [0]https://en.wikipedia.org/wiki/Citric_acid_cycle