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Malnutrition (undernutrition) is caused by a lack of nutrients, either as a result of a poor diet or problems absorbing nutrients from food.

Certain things can increase your risk of becoming malnourished.

Some health conditions that can lead to malnutrition include:

• long-term conditions that cause loss of appetite, feeling sick (nausea) and/or changes in bowel habit (such as diarrhoea and vomiting – these include cancer, liver disease and some lung conditions (such as chronic obstructive pulmonary disease)
• mental health conditions, such as depression or schizophrenia, which may affect your mood and desire to eat
• conditions that disrupt your ability to digest food or absorb nutrients, such as Crohn's disease or ulcerative colitis
• dementia, which can cause a person to neglect their wellbeing and forget to eat
• an eating disorder, such as anorexia

You can also become malnourished if your body needs an increased amount of energy – for example, if you're healing after surgery or a serious injury such as a burn, or if you have involuntary movements such as a tremor or shaking hands.

Some types of medicine may also increase your risk of developing malnutrition.

Some medicines have unpleasant side effects, such as making you feel sick, losing your appetite, or having diarrhoea, which could mean you eat less or do not absorb as many nutrients from food.

The following factors can also contribute to malnutrition:

• teeth that are in poor condition, or dentures (false teeth) that do not fit properly, which can make eating difficult or painful
• a physical disability or other impairment that makes it difficult to move around, cook or shop for food
• living alone and being socially isolated
• having limited knowledge about nutrition or cooking
• alcohol or drug dependency
• low income or poverty

In the UK, malnutrition in children is often caused by long-term health conditions that:

• lead to a lack of appetite
• disrupt digestion
• increase the body's demand for energy

Examples of these types of conditions include childhood cancers, congenital heart disease, cystic fibrosis and cerebral palsy.

Some children may become malnourished because of an eating disorder or a behavioural or psychological condition that means they avoid or refuse food.

Malnutrition caused by a poor diet is rare in the UK, but it can happen if a child is neglected, living in poverty or being abused.

Call the NSPCC helpline on 0808 800 5000 if you're concerned about a child.