Not-your-lawyer-: The nutritional information on packaging is *roughly* accurate to the amount that the average person absorbs.
The process is silly, and involves explosions and poop. Food is basically just fuel, and burning fuel can tell you how much energy was in that fuel. Scientists freeze-dry food, crush it into powder, and explode it inside a machine called a bomb calorimeter. Reading the energy released by burning the freeze-dried food gives a general idea of how much energy was in that food.
At the same time, other scientists feed that same food to people, collect their poop, and perform the same process. Freeze-dry. Crush. Explode. That gives an idea of how much energy a person does not “absorb” in the digestion process.
Subtract one from the other. Total energy minus unused energy equals energy absorbed.
Of course, this is a rough estimate, conducted for only certain foods. More complex items are just sums of the already-taken measurements for their component parts.
[[Edit: Of course these are “standard” values and the amount absorbed by any individual may vary slightly based on their own unique digestive tract & the microbes living there.]]
ashbyashbyashby: The amounts on the packaging are still accurate. This is why packages say “the average adult daily energy intake is 8700k. Yours may vary” or something to that effect. They can’t account for individuals metabolism. But they can give exact measured amounts of what’s in the food. If you know your metabolism well enough you can calculate how much/what to eat in a day by trial and error. Don’t eat sugar 😉
DonkeyTypeR: It’s safe to assume that raw ingredients have accurate nutritional specs.
The processing (baking, frying, cooking, freezing, etc) of raw materials does have an impact on final specs.
The larger the company the more likely they have the money/budget to extract more accurate results out of the final product whereas a smaller company with limited scientific resources or skills may have a product calculated based on raw ingredient specs without taking into account the processing.
TL;DR: Take nutritional specs with a grain of salt. They exist to prevent scurvy and other nutrient deficiencies.
Source: I do nutritional labeling in a small sized wholesale bakery.
Concise_Pirate: It is true your body does not absorb 100% of the nutrients you eat. The package doesn’t claim you do. It just says what nutrients are present in the thing.
warm_melody: They do tests on what is actually in the food, not on what you absorb, the labels are still ‘accurate’.
The labels are **misleading**. For items which are normally cooked after purchase (starches, proteins) you can absorb significantly (~90%) less of what it says on the tin, if you eat it raw.
steel_member: Calories intake is a measurement of energy. There are standardized test used to measure the amount of energy (in units of Cal). Similarly for composition of protein, salt, fat etc.
How your body absorbs it is not accounted for in this measurement since all our bodies are unique. That’s why you have people who can eat one cake per day and be fit while someone else may gain 30 pounds.