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

Question

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

Answer 1

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.