What are calories?

The calorie count tells you how much energy is contained in a food product. The energy in food is sometimes also measured in units called joules. When people talk about calories or joules in connection with nutrition and diet, they really mean kilocalories (thousands of calories) or kilojoules (thousands of joules). The abbreviation for kilocalories is kcal. For kilojoules it’s kJ. Calories can be converted into joules – and vice versa – as follows:

• 1 kcal is equal to around 4.2 kJ.
• 10 kJ is equal to around 2.4 kcal.

Micronutrients, alcohol and fiber provide the body with various amounts of energy:

• Carbohydrates: 4 kcal per gram (17 kJ per gram)
• Proteins: 4 kcal per gram (17 kJ per gram)
• Fats: 9 kcal per gram (38 kJ per gram)
• Alcohol: 7 kcal per gram (29 kJ per gram)
• Fiber: 2 kcal per gram (8 kJ per gram)

These are averages. The amount of energy your body can actually use depends on various factors.

Total potential energy is the complete amount of energy found in a food product. Scientists calculate it by burning the product in a lab.

Our bodies “burn” food products too. But they can’t consume all the energy because they need some of it to be able to digest the food. A small part of the total energy also passes straight through as waste. The energy that our bodies can extract from a food product is what is known as the “physiologically available energy.” It is slightly lower than the total potential energy.

The exact amount depends on the structure and composition of the food product, how it was prepared and the person’s gut flora. It varies from person to person and is linked to eating habits.

Calorie charts can help you get an idea of the energy food products supply. But the information isn’t 100% accurate – partly because food products aren’t always the same. For instance, the nutrient content in fruit and vegetables can differ depending on variety, weather, soil and ripeness.

The figures in the following tables are rounded averages.

In the European Union, the labeling on packaged food has to show the energy per 100 grams or 100 milliliters. Manufacturers have to include information about the fat, saturated fatty acids, carbohydrates, sugar, protein and salt contained in the product too.

The label often also says how many calories there are in one serving. If it does, it’s a good idea to check the size of the serving. Sometimes it’s smaller than what you’d normally eat – half a frozen pizza, for example. Or much smaller than the serving shown on the packaging.

But you can get a good feel for how many calories there are in something (a cup of rice, for example) by weighing the servings you eat.