Final answer:
Calories on food labels represent the energy content of the food, which our bodies can use for various functions. These Calories are actually kilocalories, and the energy content is calculated using the average caloric values of proteins, carbohydrates, and fats present in the food.
Step-by-step explanation:
On a food label, Calories measure the amount of energy provided by the food. This is the energy that our bodies can use for all bodily functions and activities. The term 'Calories' on labels actually refers to kilocalories (kcal), which are units of 1000 calories. To calculate the caloric content, nutritionists apply the Atwater system, which uses the average caloric content of the main macronutrients: proteins, carbohydrates, and fats. For example, the total energy for a portion of food can be determined by multiplying the amount of protein, carbohydrates, and fat by their respective average Calories per gram, and adding these together.