How do "they" know how many calories/fat/nutrients are in each food item before they put it on the label?

Send a serving to the lab?

@MyNewtBoobs I would think so, too. But, do calories have specific molecules? I don’t understand how it works. I haven’t been to school in a long, long time. :)

@ANef_is_Enuf I don’t know, but maybe they just know that fat and glucose and the like have calories (I think) and measure how much of those are in there?

Nutrition labels

They burn a sample in a bomb calorimeter.

Burn the food to determine the calories (energy), and I assume the rest of the information is gathered via information on the ingredients and/or other tests to determine the levels of those other chemicals.

They burn some to figure out the caloric value, which means it isn’t an accurate measure of how much energy we get from it.

Same reason labs can find out what’s in your blood.

Chemistry.