How your body uses food

A balanced diet will provide you with everything you need to keep your body working well. Foods fall into different groups, all of which are used in a specific way by our bodies. They include:

  • Carbohydrates – they turn into glucose to give us energy. Energy is measured is calories. If we have too many calories, we put on weight. Men need about 2,500 calories a day and women about 2,000.
  • Proteins – the amino acids they contain help the body build muscle and repair tissue. When we’re unwell, it’s important to have proteins.
  • Vitamins and minerals – they help our bodies work normally. Minerals help maintain healthy bones and nerves for example.
  • Fats – they bring condensed energy to the body.
  • Fibres – they are a good source of iron and vitamin B and give us energy.
  • Fluid – to function properly the body needs fluid. You should aim to drink 1.5 litres of fluid every day.

How foods are used in our bodies

Food has nutrients in it that our bodies need. The main groups of nutrients are carbohydrates, proteins, vitamins and minerals, fats, fibre and fluids. A healthy diet gives you all of the nutrients you need to keep your body working well. For most people, a balanced diet includes:

  • lots of fruit and vegetables
  • plenty of starchy (carbohydrate) foods such as bread, rice, pasta, noodles, couscous and potatoes
  • some protein-rich foods such as meat, poultry, fish, nuts, eggs and pulses (beans and lentils)
  • some milk and dairy foods such as cheese, yoghurt and cream
  • just a small amount of food high in fat, salt and sugar.

Drinks should mainly be water, tea and coffee (without sugar), or sugar-free drinks such as fizzy drinks, colas and squashes.


Carbohydrates are broken down in the body to become glucose, which gives us energy. Energy is measured in calories. We all need a certain number of calories each day for energy, even if we aren’t being very active. For example, we need energy to breathe when just sitting in a chair.

The amount of energy a person needs each day varies. It depends on how quickly their body uses the energy, and on their level of activity. An adult man needs about 2,500 calories a day and an adult woman needs about 2,000 calories. If we have too many calories, we put on weight. If we don’t have enough, we use up our body’s energy stores and lose weight.


Proteins are made up of amino acids. Our bodies use amino acids to build and repair muscles and other body tissues. We need extra protein (as well as extra energy) when we are ill, injured or stressed to repair any damage.

Vitamins and minerals

Vitamins are essential in helping our bodies work normally, but we only need tiny amounts of them. If you’re eating even a little of the main foods that contain vitamins, you’re probably getting a good enough supply. But if you’re not able to eat well for a long period of time, you may need multivitamins to top up your body’s stores. Your doctor, dietitian or pharmacist can give you advice about these.

Minerals are substances needed by the body for various functions, such as maintaining healthy nerves and making bones and teeth.


Fats provide a concentrated source of energy and contain some important vitamins.


Fibre is sometimes called roughage. It’s the part of the food that passes through the body without being completely absorbed. Choose wholemeal bread, chapatis and pittas; wholegrain cereals and pasta; brown rice; and yams and potatoes with their skins on. These provide energy and are also a major source of iron and B vitamins. Fruit and vegetables are good sources of fibre too.


Our bodies need a certain amount of fluid each day to work properly. It may be difficult to drink enough liquid when you don’t feel well. Women should try to drink roughly 8 glasses (about 1.6 litres) of fluid a day, and men should try to drink about 10 glasses (about 2 litres) a day.

This can be any type of fluid. Water is the best for hydration but contains no extra nutrients such as energy or vitamins. Milk, smoothies and pure fruit juices contain a lot of energy and nutrients so they may be good choices if you are struggling to eat well. Soft and fizzy drinks that contain a lot of sugar are high in energy, but they don’t contain any other nutrients. The sugar and acidity may also harm your teeth.

Drinks that contain caffeine include coffee, tea and some fizzy drinks. These may dehydrate you because they make you produce more urine. You can include them as part of your normal fluid intake, but drink other fluids that don’t contain caffeine as well.

Back to Preventing weight loss

The building-up diet

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Shopping list

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You can increase your energy intake by preparing your meals slightly differently. Our menus offer some suggestions.