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What is it?

The word "malnutrition" literally means “bad nutrition”. The body needs a certain amount of food and other nutrients to function, and a person who does not receive the required amount of food and nutrients is said to be “malnourished”. Malnutrition can be caused by undernutrition (when the body receives less food and nutrients than it needs) or overnutrition (when the body receives more food and nutrients than it needs). Commonly when people refer to malnutrition they are really referring to undernutrition (wasting, stunted growth or micronutrient (e.g. vitamin) deficiencies). This will be the main focus of this topic.

Chronic overnutrition is common in many countries, and it can lead to obesity and to metabolic syndrome, a set of factors that increases the risk of certain health problems and is characterised by abdominal obesity, a decreased ability to process glucose (insulin resistance), dyslipidaemia (unhealthy lipid levels), and hypertension. People with metabolic syndrome have been shown to be at a greater risk of developing type 2 diabetes and cardiovascular disease. Another relatively uncommon form of overnutrition is vitamin or mineral toxicity, which is usually caused by taking too many supplements (for instance, high doses of fat-soluble vitamins such as vitamin A). Toxicity symptoms depend on the substance(s) ingested, the severity of the overdose, and whether the toxicity is acute or chronic.

Undernutrition occurs when the body does not have enough vital nutrients to develop and function normally. These may be macronutrients (protein, carbohydrate and lipids (fats)) or micronutrients (vitamins, minerals and trace elements). This may be due to:

  • The body not receiving enough nutrients
  • The body losing more nutrients than usual
  • The body demanding more nutrients than usual
  • The body not being able to digest and absorb nutrients because of a condition or a disease

Although the body always needs adequate nutrition, its requirements vary, both on a daily and a yearly basis.

  • During infancy, adolescence and pregnancy, people need extra nutrition for normal growth and development. In children, a severe shortage of food will lead to a condition called marasmus, which is characterised by a thin body and stunted growth. Children who consume enough calories but do not eat enough protein may develop kwashiorkor – a condition characterised by oedema (fluid retention), an enlarged liver, lethargy and delayed development. If a child's diet does not provide them with enough vitamins, their bones and tissues may not develop normally. A lack of vitamin D, for instance, can affect bone formation, – causing rickets in children and osteomalacia in adults. A eficiency in folic acid during pregnancy can cause birth defects.
  • Acute conditions such as surgery, severe burns, infections and trauma can drastically increase (in the short term) the amount of nutrients the body requires. Patients who have been malnourished for some time may have compromised immune systems and thus be less able to fight off infections. They frequently take longer to heal after surgical procedures and must spend more days in the hospital. For this reason, many doctors and dietitians screen and monitor the nutritional status of their hospitalised patients. Patients having surgery are frequently evaluated both prior to surgery and during their recovery process.
  • Chronic diseases may be associated with the body losing nutrients and/or needing more nutrients, and with malabsorption (the inability of the body to absorb and use available nutrients). Malabsorption may occur with chronic diseases such as coeliac disease, cystic fibrosis, pancreatic insufficiency and pernicious anaemia. People with chronic kidney disease, diarrhoea and chronic blood loss will lose nutrients more quickly than usual. Sometimes, medical conditions and/or their treatments can cause malnutrition because they affect the amount of food people eat. For example, they may reduce the appetite, they may make it difficult to swallow, or they may cause nausea (which is associated both with cancer and chemotherapy, and with HIV/AIDS and its drug therapies). People who chronically abuse drugs and/or alcohol may also lose nutrients more quickly than usual, and/or may ingest fewer nutrients, and their bodies may struggle to absorb and use available nutrients.
  • Elderly patients require fewer calories but they still need to ingest an adequate amount of food and nutrients. They are often less able to absorb nutrients (in part because of decreased stomach acid production) and they are more likely to have one or more chronic ailments that may affect their nutritional status. They may also have more difficulty preparing meals and less access to a variety of nutritious foods. Older patients also frequently eat less due to a decreased appetite, a decreased sense of smell, decreased emptying of the stomach and/or difficulties with chewing or swallowing.

Last Review Date: September 5, 2017