How can they tell how many calories are in different foods?
(Lansing State Journal, June 28, 1995)
The Calorie (spelled with a big "C") that we speak of when talking about food is actually the kilo calorie or in other words, 1,000 calories (spelled with a small "c"). The calorie is a unit of energy.
Because the processes of burning food and digesting food release the same amount of energy overall, we can burn food to measure the number of Calories there are in food. Most of the time the food first has to be dried so it will burn easily. The food is put in a container with plenty of oxygen which is in turn placed in a know n amount of water. The food in then ignited and the change in water temperature is measured as the food burns. Because we know how much energy it takes to raise water's temperature, we can determine how much energy was released by the food when it was burned. This is the same amount of energy that will be released when the food is digested.