Calories are a measure of heat. Not Energy. You measure calories buy burning the food in question and measuring how hot it raises the temperature of a given amount of water.
Magnesium burns a lot hotter than corn therefore it has far more calories than corn yet eating a pound of magnesium a day is not going to make you as fat as a pound of corn a day.
So please stop with the "calories in, calories out" simplification.
Calories ARE a measure of energy. One calorie = 4.2 joul = 4.2 wattsecond.
A calorie is defined* by the amount of energy needed to heat 1 gram of water by 1 degree celsius under a pressure of 1 temperature. But heat is energy, and a calorie (as well as a joul) are a measure of both.
> So please stop with the "calories in, calories out" simplification.
That part is true: Calories in, calories out is wrong, as has been shown repeatedly over the last 50 years. But somehow it is still the religious belief of many.
I should been clearer. I meant "energy" in terms of energy the body can use. E=MC^2 means everything can be considered energy. But can something be used as energy for a specific process, like making a body fatter, is another issue.
We agree, calories do not measure how much energy the body can extract or use from a piece of food. They only measure how much energy is produced burning the food. Bodies don't burn food, they digest it. So measuring calories doesn't say anything about whether a particular substance can be used by the body.
> They only measure how much energy is produced burning the food. Bodies don't burn food, they digest it.
You need to review your biology. The most common energy extraction process in the body actually IS, at its essence, oxidation - a.k.a "burning". And that's why people did the calorimeter burning measurements. The other common process is essentially fermentation, but in a healthy human, the vast majority of energy is obtained from food through oxidation.
> So measuring calories doesn't say anything about whether a particular substance can be used by the body.
It puts an upper limit because (as far as we know) oxidation is the most efficient process the body uses, but not a lower limit.
The body may flush out anything without any form of digestion, fat conversion, or oxidation (thus no energy extraction), even if it is pure sugar. Furthermore, the enzymes used by the body for oxidation are very specific. The most abundant carbohydrate around us, cellulose (wood and paper are examples), cannot be digested / oxidized / burned by the human body.
Magnesium burns a lot hotter than corn therefore it has far more calories than corn yet eating a pound of magnesium a day is not going to make you as fat as a pound of corn a day.
So please stop with the "calories in, calories out" simplification.