You’ve likely heard about the metric equivalent of joules, the unit of energy measurement. A calorie is the energy needed to raise the temperature of 1 gram of water by 1 degree Celsius.
The amount of energy required to maintain health and fuel the body is much greater than the small number of calories needed to heat a gram of water. The term “calorie” is used in nutrition to refer to a kilogram calorie, which is 1000 calories. If you see “calories” on a nutrition label, it is likely to be kcals.
When the body breaks down carbohydrates, proteins, fats, and alcohol, the stored energy in food is released. The body uses this energy to perform activities like keeping our hearts beating, our lungs breathing, and our muscles in motion.
Energy in food is measured by the amount of energy that food and beverages provide to these bodily functions. The four macronutrients contain varying amounts of energy.
How do you estimate calories?
You can estimate the energy content of food and beverages in two different ways.
First, there is “bomb calorimetry.” The gold standard method is to place a small amount of food or beverage inside a device called a bomb calibrator. In the presence of oxygen in the food, heat is released.
This method is used to calculate the energy content of food by calculating the heat release. This method is used most often for foods that are high in fats. It is also the most expensive method.
The second method is the Atwater System, which is much cheaper. This method is used more often to calculate the energy content of food and beverages sold in supermarkets. This system, named after the legendary food researcher Wilbur Atwater, uses a conversion factor to convert each macronutrient into food and drink. Estimating the amounts of each macronutrient allows an approximation of total energy.
This method, however, requires a detailed understanding of the components in composite foods (such as a muesli bar or hamburger), which can reduce accuracy. The Atwater system also has a margin for error, as it assumes that each ingredient will always be the same.
Due to differences in soil and climate, a cup of oats from one region of the country may not have the same nutritional value as another cup of oats from another part of the nation. This system is based on averages.
Both methods estimate the energy of foods and drinks. The amount of energy that our bodies actually extract from food and drink can vary depending on factors like individual differences in digestion, absorption, and food processing.
Why are calories printed on foods?
In Australia, it is a requirement that packaged food products have a nutrition panel that shows the number of calories it contains.
A nutrition panel may not be required for homemade food sold in places such as a fresh market. The type of food sold and the size of the business will determine whether a nutrition information panel is required.
Fresh foods such as fruits, vegetables, and meat do not require nutrition information panels. You can use a bomb calorimeter to find out how many calories are in the food, or you can look it up in an online database.
These databases, such as CalorieKing, compile data about the energy and nutritional content of different foods. Dietitians and health professionals often use these databases to estimate the energy contents of foods in order to make dietary recommendations.
Different international standards
Both kJ (energy) and kcal (energy) are different measurements. They are similar to how centimeters and inches are other units when measuring length. Kilojoules is a part of the International System of Units.
Australia, New Zealand, and parts of Europe are using kJ. The United States and the United Kingdom use kcal. You can convert between kilojoules and calories using the conversion factors.