Last Review Date: September 5, 2017

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.

Signs and symptoms

General malnutrition often develops slowly, over months or years. As the body’s store of nutrients is depleted, changes begin to happen at the cellular level, affecting biochemical processes and decreasing the body’s ability to fight infections. Over time, a variety of symptoms may begin to emerge depending on the particular nutrient deficiency, including:

  • Weight loss, decreased muscle mass, decreased subcutaneous fat and weakness
  • Growth retardation or failure to thrive (in children)
  • Oedema (swelling, due to lack of protein)
  • Poor wound healing
  • Anaemia (iron deficiency, vitamin B12 deficiency)
  • Dry, scaly skin
  • Hair loss
  • Brittle and malformed (spooned) nails (iron deficiency)
  • Chronic diarrhoea
  • Bone and joint pain
  • Mental changes such as confusion and irritability
  • Goitre (enlarged thyroid)

Specific nutrient deficiencies may cause characteristic symptoms. For instance, vitamin B12 deficiency can lead to tingling, numbness and burning in the hands and feet (due to nerve damage), a lack of vitamin A may cause night blindness and an increased sensitivity to light, and a lack of vitamin D can cause bone pain and malformation. The severity of symptoms depends on the intensity and duration of the deficiency. Some changes, such as to bone and nerves, may be irreversible.


Malnutrition will often be noticeable to the doctor’s trained eye before it causes significant abnormalities in laboratory test results. During physical examinations, doctors and dieticians will evaluate patient's overall appearance: their skin and muscle tone, the amount of body fat they have, their height and weight, and their eating habits. In the case of infants and children, doctors and dieticians will look for normal development and a normal rate of growth.

If there are signs of malnutrition, the doctor may order general laboratory screening tests to evaluate a patient’s blood cells and organ function. Additional individual tests may be ordered to look for specific vitamin and mineral deficiencies. If general malnutrition and/or specific deficiencies are diagnosed, laboratory testing may be used to monitor how the patient responds to treatment. A person who has malnutrition because of a chronic disease may need to have his or her nutritional status monitored on a regular basis.

Hospitalised patients are often assessed to determine their nutritional status prior to, or at the time of, admission. This may include discussing their medical history with a doctor, being interviewed by a dietician, and undergoing some laboratory tests. If the results of these tests indicate possible nutritional deficits, patients may be provided with nutritional support (i.e., given the nutrients they need) prior to a surgery or procedure, and they may be monitored regularly during recovery.

Laboratory tests may include:
For general screening and monitoring:

For nutritional status and deficiencies:

  • Prealbumin (also used to assess protein status, as it rises and falls more rapidly than albumin and can be used to detect short-term response to treatment)
  • Iron tests (such as iron, TIBC and ferritin)
  • Vitamins and minerals (such as B12 and folate, vitamin D, vitamin K, calcium, and magnesium)
  • Trace elements such as zinc and selenium are important for patients on long term parenteral nutrition

Non-laboratory tests
Imaging and radiographic scans may be ordered to help evaluate the health of internal organs and the normal growth and development of muscles and bones. These tests may include:

  • X-rays
  • CT (computed tomography)
  • MRI scan (magnetic resonance imaging)


Treatment of undernutrition includes:

  • Replenishing the nutrients that are missing, making nutrient-rich foods available and providing supplements for specific deficiencies. In someone who is severely malnourished, this must be done slowly until the body has had time to adjust to the increased intake. It must then be maintained at a higher-than-normal level until a normal or near-normal weight has been achieved.
  • Regular monitoring of patients with chronic malabsorption disorders or protein- or nutrient-losing conditions. Once the deficiencies have been addressed, a treatment plan will need to be put in place to prevent the malnutrition from recurring.
  • Addressing any social, psychological, educational and financial issues that may be causing or exacerbating the malnutrition, such as access to nutritious food.

Related pages

On this site
Tests: Albumin, FBC, electrolytes, iron tests, lipid profile, urinalysis, prealbumin, vitamin D, vitamin B12 and folate
Conditions: Metabolic syndrome, alcoholism, coeliac disease, cystic fibrosis, diarrhoea, HIV, pancreatic insufficiency, pregnancy

Elsewhere on the web

Healthdirect Australia - malnutrition



Additional article used in this review
Nieuwenhuizen, W.F., Weenen, H., Rigby, P., Hetherington, M.M. Older adults and patients in need of nutritional support: Review of current treatment options and factors influencing nutritional intake. Clinical Nutrition. 2010 29(2):160-169

References from Lab Tests Online-US
Primary sources of information for Malnutrition