What are “Calories”

Calories like kilojoules are “units” expressing the energy stored in food. To avoid potential confusion when reading food labels and embarking on exercise campaigns, it is important to understand what these units mean and how they inter-relate.

The word energy comes from the ancient Greek work “energeia”, meaning activity or operation. We need energy to breathe and to go to work and even sleep.

Human beings need energy to survive and thrive. Energy is the magic behind the scenes ingredient that gives your heart the ability to regularly beat while pushing and forcing blood over large distances every day.


Energy is equivalent to mass or put another way, matter can be converted to energy. Humans have been blessed with a way of extracting energy from matter and we do this through two activities we take mostly for granted — breathing and eating. Alternatively, respiration and digestion unlock the energy stored in the molecules of food — a micro energy release occurs as oxygen in our breath combines with the carbon atoms in food.

This released energy drives essential processes in our body — cell replication and growth, muscle contraction, expansion and movement and importantly a 24/7 active pumping system that pushes nutrients across cell membranes and into the cell while at the same time pushing waste products and toxins out of the cell.

Basic metabolic Rate

These processes all require varying amounts of energy. We consume significant amounts of energy doing absolutely nothing. Just breathing and sleeping. This is called our basic metabolic rate. As soon as we get up, a greater amount of energy is used dependent on the type of work we do. See next articles called “How Many Calories”

The unit used to express the amount of energy CONSUMED in these varying activities is either the calorie or kilojoule. These same units also express the amount of energy potentially STORED in food.

What are Kilojoules

Calories are the pre-metric units expressing energy. They came from experiments with heat in 1824. To raise the temperature of 1 gram of WATER by 1 degree centigrade needed 1 “small calorie” of energy. This is expressed as “cal” with a SMALL “c”.

Similarly a large calorie or also known as a food calorie or dietary calorie is expressed as Cal with a LARGER “C” and is the energy need to raise the temperature of 1 litre (=1000grams) of water 1 degree centigrade. Therefore 1000 small calories equal 1 kilocalorie or 1 large Calorie

Because 1 small calorie is often to small a unit in a nutrition context the large Calorie is nearly always used. It is however not called a large Calorie but rather just a Calorie.

The kilojoule is also used to express energy stored in food and is part of the International System of Units, abbreviated SI units. It is interchangeable with the Calorie based on the following conversion factors.

Converting Calories to kilojoules

Importantly 1 small calorie equals 4.184 joules of energy

1 Calorie (large Calorie) equals 4.184 kilojoules of energy

Converting kilojoules to Calorie

1 kilojoule equals 0.239 Calories of energy

1 joule equals 0.239 calories of energy

America still uses the Calorie unit. Australia mostly uses the kilojoule while Europe uses both. However modern dialogues on diets, weight loss and exercise, even in Australia, use Calories. Have we navigated the rough waters of calorific confusion safely and finally landed on the dry land of nourishing clarity? I hope so.