How does the FDA (or whoever does it) figure out the amount of calories in a natural food?

Im pretty sure you can't SEE it. Or weigh it... So, how's it done?How does the FDA (or whoever does it) figure out the amount of calories in a natural food?
the world will never knowHow does the FDA (or whoever does it) figure out the amount of calories in a natural food?
They feed it to someone and then see how long it takes it to burn off. Or they use some scientific process, I really don't know.
By Burning


A calorie is the amount of energy needed to heat 1 gram or oz...i cant remember up 1 degree centigrade


So you burn said food under a container of water and measure the amount of change between the original water temperature and the temp. after the burning of the food


I did this experiment in my science class.
Basically what djlugo99 said. The process is done with an instrument called a calorimeter.