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

Proteins are normally measured by determining the nitrogen content and multiplying it with 6.25 which is a very rough estimate of the weight of protein as compared to the weight of nitrogen.

Fibre, carbohydrates and sugars are all carbohydrates and can be measured crudely by subtracting the weight of water (evaporated at 105 deg C), ash (what remains after 550 deg C incineration) and protein. Alternatively carbohydrates can be quantified based on their ability to absorb light.