system
Given the following post, respond as if you're commenting on Reddit:
human
How do they figure out how many calories are in my food?
gpt
Calories are a measure of energy contained in the food.

To calculate the amount of energy in the food we need to release it. This is done by burning it completely in an oxygen atmosphere.

To measure how much energy is released they may use something called a "bomb calorimeter." Basically it is a chamber (in which a known weight of food is burned) surrounded by a known amount of water. They measure how much the temperature of the water increases. By knowing some properties of the water, how much water there is and how much the temperature of the water increases, they can calculate how much energy was released by burning the food. One calorie is the amount of energy needed to heat 1L of water from 14.5ºC to 15.5ºC.