Foods are made from substances called nutrients which form naturally. For example a plant makes food from water in the soil and carbon dioxide in the air. It uses energy in sunlight to make the food and also stores some of the energy from the sunlight in the food. In fact most plants make two foods. The first one it makes is sugar. This food is difficult for the plant to store so it changes it into another substance which can be stored more easily. This second food is starch. Both foods have similarities and we put them together in a food group called the carbohydrates.

There are other natural substances which form or collect in the bodies of plants and animals that are needed in our food. We divide them into four more food groups. These groups are fats, proteins, vitamins and minerals.

Each food group provides the body with something it needs. Carbohydrate contains a large amount of energy. It is broken down quickly by the digestive system. This means that the energy can be released quickly for the body to use.

Fat contains even more energy than carbohydrate. The body cannot release the energy from the fat quickly so it uses fat as an energy store. The body needs a certain amount of energy all the time to keep it alive. Normally the food in a meal will supply enough energy for all the body's needs. If a person has to go without a few meals he or she will feel hungry but will survive because the body will use energy stored in the fat to keep all its life processes going.

Protein contains some energy but it also contains materials which the body can use to grow and to repair itself.

Vitamins do not provide energy or materials for growth. They are substances which make parts of the body such as the eye or the nerves work properly. They also make the body grow and maintain itself properly. For example a lack of one vitamin makes the leg bones soft and bendy in children while the lack of another makes the skin become flaky and makes the gums bleed.

Minerals help the body in two ways. They help it grow and they help it work properly. Some minerals such as calcium help in both ways. It is needed for the growth of bones and teeth and it is needed to help blood clot and for muscles to move. Iron is another mineral. It is not needed for growth but for helping the blood carry oxygen round the body.

There is not one food which contains all the food groups in the amounts we need so we have to eat a selection of foods.