How are we able to calculate macronutrients and calories in foods?


A friend of mine and I were chatting about how interesting it is that almost every food has a nutritional facts sheet, detailing its contents of macro and micro nutrients. That then branched out to the conversation on how we calculate a food’s nutritional value such as calories and macronutrients (carbs, fats, protein). How were we able to detect what foods were made up from based on so little information before the technology we have today?

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Macronutrients (Carbs, Fats, Proteins): These are measured using chemical analysis techniques. For example, proteins can be measured by assessing the nitrogen content of a food (since proteins are made up of amino acids, which contain nitrogen). Carbohydrates and fats are usually measured through chemical reactions that can identify and quantify these specific compounds.

Micronutrients (Vitamins, Minerals): These are also measured with various chemical analysis techniques. For example, vitamin C content might be measured using a process called titration, which can identify the amount of a particular substance (vitamin C, in this case) in a solution

For routine foodstuff labeling, a whole bunch of simplifying assumptions and shortcuts are involved.

Proteins are determined by measuring total nitrogen, then assuming that any detected came 100% from proteins, and that the amino acids in that protein are a typical distribution.

Fat is determined by extraction with a hydrophobic solvent, followed by drying and weighing. It’s assumed that anything extracted must be fat.

Carbohydrates aren’t directly measured at all, but are back calculated by subtracting protein, fat, water and ash after burning.