ELi5: How do they measure calories etc for nutritional labels?


I always wonder how “they” can know the exact amount of fiber, protein, carbs and sugars, etc when I’m reading ingredient labels.

PS: couldn’t decide between biology or chemistry flair since I guess my question relates to biochemistry! Haha

In: 527

They burn the (dried) food and measure how much heat it gives off.

Thats done by putting it in a bucket of water and measuring the water temperature before and after.

This is done to a lot of basic foods and written down and published and im sure many companies just estimate based on ingedients. Not everyone is measuring themselves.

It depends a lot based on gender, genetics, health conditions, and goals. Calorically depends a lot if you aim to lose weight or gain. High protein is important if you aren’t sedentary or exercise. Carbs and sugars are more particular unprocessed vs processed foods/simple vs complex carbs. Complex require more energy to digest and are recommended for consumption over simple but it’s about moderation. There’s also calories you burn by just living called Basal Metabolic Rate which differs by each person. Essentially, pick high fiber and protein packed foods and mostly avoid high sugar and processed foods. Sugar is fine in fruit imo. If weight loss is your goal, counting calories is now seen as counterintuitive mental health wise but you burn more calories than consumed=equals weight loss. Factor in muscle growth in terms of weight if you lift.

I remember my chemistry book depicted a testing apparatus for determining caloric content of food. The short answer is they burn it in an essentially oxygen-rich, closed environment that’s surrounded by a known quantity of water. The experiment measures the temperature change of the water, after the dried food sample is burned. The definition of a Calorie gives us a hint: “a unit of energy, often used to express the nutritional value of foods, equivalent to the heat energy needed to raise the temperature of 1 kilogram of water by 1 °C, and equal to one thousand small calories” from the Oxford English Dictionary.


You can do this in a lab, but it’s expensive and slow so a food business will almost always just calculate calories etc based on the ingredients and a list of standard measurements, with an app of some sort ([like this one](https://www.food.gov.uk/business-guidance/menucal-calorie-and-allergen-tool)).

The list is made from actual lab measurements using a calorimeter to basically burn the ingredient and measure the energy released. They often include other facts like vitamin content and so on.

Here’s the one for the UK (the USDA and other agencies have similar ones ): https://www.gov.uk/government/publications/composition-of-foods-integrated-dataset-cofid.

(To help make these measurements repeatable, you can buy or prepare ISO-standard formulations of basic foods! They are made in a lab, quite expensive, and very plainly packaged)