Question

This is intended to be a fun question. Calorimetry used for calculating the heat generated from chemical changes has been around for centuries, however, I suspect the process for calculating food calories is much more complicated. Can anybody provide a clear succinct, knowledgable answer? Although I will accept answers with links, an independent answer would be preferred.

Answer 1

There's a few different ways of defining what you mean by 'Calories' in food. There's the obvious physical/chemical definition of energy stored in the food, but I had an objection when I explained that warmer food naturally has more Calories than cold food. There's also the measure of absorbtion, or 'digestibility', which can be determined by what nutrients pass through the body unabsorbed.

The US FDA has guidelines that basically suggest for their labeling requirements, it's based on estimates of calories in the component parts of the food:

L12. Is it necessary to include a calorie conversion footnote which states that fat, carbohydrate, and protein furnish 9, 4, and 4 calories per gram, respectively?

Answer: No, the use of that footnote is optional. 21 CFR 101.9(d)(10)

But they also have rules on rounding:

L31. What are insignificant amounts of nutrients?

Answer: These are the amounts that are permitted to be shown as zero on the Nutrition Facts label (e.g., less than 5 calories may be expressed as 0 calories) except that for total carbohydrate, dietary fiber, and protein, it is the amount that can be declared as