In the UK, almost 7 in 10 men and almost 6 in 10 women are either overweight or obese. This means that many of us are consuming more energy (calories) than we need from food and drinks. This article will explain the concept of energy and how it impacts on bodyweight.

1. Energy density

2. Energy requirements

3. Energy balance


Energy density

We all need energy to grow, stay alive, keep warm and be active. Energy is provided by the carbohydrate, protein and fat in the food and drinks we consume. It is also provided by alcohol. Different food and drinks provide different amounts of energy. You can find this information on food labels when they are present.

Energy is measured in units of kilocalories (kcal) or kilojoules (kJ).

One kilocalorie (1 kcal) is equal to 4.18 kilojoules (4.18 kJ).

  • Fat contains 9 kcal (37 kJ) per gram

  • Alcohol contains 7 kcal (29 kJ) per gram

  • Protein contains 4 kcal (17 kJ) per gram

  • Carbohydrate contains 3.75 kcal (16 kJ) per gram (for the purposes of food labelling this is rounded up to 4 kcal per gram)

The amount of energy a food contains per gram is known as its energy density so we can describe fat as more energy dense than protein or carbohydrate. You can find out more about why we need carbohydrate, protein and fat in our diet and in which proportions here.

How is energy content calculated?

The total energy content of a food can be found by burning it and measuring how much heat is released.

Foods with fewer calories per gram such as fruits, vegetables, low fat soups, lean protein and fibre-rich foods have a relatively low energy density.

Foods with a high fat and/or low water content such as chocolate, cakes, biscuits, deep fried foods and snacks, butter and oils, have a relatively high energy density.

Basing your diet on foods which are lower in calories (or have a lower energy density), and eating foods which are high in calories (or have a higher energy density) less often and in small amounts, can help to control you overall calorie intake. Some foods with a higher energy density such as oily fish, cheese, nuts, seeds and avocados contain healthier types of fat and other important nutrients meaning they can be consumed in moderate amounts as part of a healthy, balanced diet. You can find out more about energy density here and making small changes to help you lose weight here.

 Next: Energy requirements