Our bodies need energy to grow and repair themselves, keep warm and do physical activity. Energy comes from food and drinks, in particular from carbohydrateproteinfat and alcohol. Carbohydrate, protein and fat are essential which means we need them in our diet to survive and function, whereas alcohol is non-essential (we do not need it in our diet to survive and function). This energy is measured in kilojoules (kJ) or calories (kcal), with 1 kilocalorie equalling 4.2 kilojoules. In nutrition, calorie and kilocalorie are sometimes used to mean the same thing, for example, if someone says ‘an apple is ~100 calories’ the accurate statement would actually be ‘an apple is ~100 kilocalories’.

Energy values of different nutrients

NutrientEnergy provided
Carbohydrate17kJ (4 kcal) per gram
Protein 17kJ (4 kcal) per gram
Fat37kJ (9 kcal) per gram
Alcohol29kJ (7 kcal) per gram

As you can see, fat contains more than twice as much energy as carbohydrate and protein, closely followed by alcohol. This needs to be taken into account when we are watching our weight, or trying to reduce it.

Energy density

Food and drinks are made up of different amounts of protein, fat, carbohydrate (and sometimes alcohol); known collectively as macronutrients. The amount of each macronutrient in the food will determine its energy content.
Foods that are high in kilojoules per bite, tend to be high in fat and/or sugar (for example, chocolate, fizzy drinks, fats and oils). Such foods are described as energy-dense.
Low energy-dense foods (for example fresh fruit, vegetables and porridge) have fewer kilojoules in each bite and tend to fill you up for longer.
But remember it is not only the type of food that we eat but how much – a large plate will have more energy (kilojoules) than a smaller portion. 

How much energy do I need?

How much energy you need is dependent on your gender, age, weight, and how active you are. If you are particularly active or play sport, visit our sports nutrition page for information on meeting your energy needs.

Men require more energy than women, and we tend to need less energy as we age due to a decrease in muscle mass. Teenagers have large energy needs to cater for all the growing they are doing.


To maintain a healthy body weight, we should only consume as much energy as we need. Unused energy is stored as fat which accumulates over time, causing weight gain.

If you would like more information on your energy intake or energy requirements, contact a dietitian/nutritionist who can assess your needs and advise you accordingly. 

Last modified: January 27, 2022