Essentially, a calorie is no more than a measurement of energy in the form of heat.
“The calorie is a pre-SI metric unit of energy. It was first defined by Nicolas Clément in 1824 as a unit of heat, entering French and English dictionaries between 1841 and 1867. In most fields its use has been replaced by the SI unit of energy, the joule….
Definitions of the calorie fall into two classes:
So, calories are a measurement of heat.
If you would like to know how many calories are in a hamburger, you would place it in a metal box called a calorimeter, set it on fire and measure how much heat it produces.
So the question that you must ask is “have you ever eaten a hamburger and set it on fire in your stomach for it’s heat?” I would assume that you have not.
The assumption in measuring calories, nutritionally speaking, is that since your body produces heat as a byproduct of its metabolism, that you can use this to predict metabolic demand and supply. The problem is that the heat is merely a byproduct. ATP is the primary product. Using heat to predict ATP supply and demand is highly inaccurate and can vary significantly from individual to individual and even across and individual’s life.
The body’s demand for protein, fat, and carbohydrates is a far more predictable way to measure energy intake and demand.
By Jeremiah Jacobs