Subreddit: r/AskScience
User: u/stalkythefish
Original Post:
Do the calorie counts on food account for the undigestible parts that pass through, or is it just "We burned this to ash and got this many calories out of it."?
My Response:
Usually we just say we burned it to ashes in a bomb colorimeter and call it a day. Also have to subtract out the energy content of fibers and other indigestibles. The truth? As a food scientist, I construct nutrition labels pretty often. If it’s not a novel food, I just pull up the USDA Nutrition Database and back calculate the caloric content knowing the composition of the food product. It’s a very crude and simple system, mostly because it’s very costly to run a bomb colorimeter on a food product, and you’re probably creating multiple variations of a food formulation.
You’re allowed about 10% difference between the calculated and actual calorie content of the food. You’re also likely to be rounding anyway; usually the case if the concentration of certain caloric components (such as sugars) fall below a certain threshold.
It’s funny, so things like allulose and certain fibers actually have some caloric content, generated primarily from the metabolism of the components in the gut microbiome and converted into acetic and butyric acids. But we just don’t count them because it’s about 10% the energy content in these that’s converted into human energy.
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