This article was last reviewed on
This article waslast modified on 19 September 2023.
What is it?

Malnutrition is a disparity between the amount of food and other nutrients that the body needs and the amount that it is receiving. This imbalance is most frequently associated with under nutrition, the primary focus of this article, but it may also be due to over nutrition.

Chronic over nutrition can lead to obesity and to the metabolic syndrome, a set of cardiovascular risk factors characterised by abdominal obesity, a decreased ability to process glucose (insulin resistance), dyslipidaemia, and hypertension. Those 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. This is usually due to excessive supplementation, for instance, high doses of fat-soluble vitamins such as vitamin A rather than the ingestion of food. Toxicity symptoms depend on the substance(s) ingested, the severity of the overdose, and whether it is acute or chronic.

Under nutrition occurs when one or more vital nutrients are not present in the quantity that is needed for the body to develop and function normally. This may be due to insufficient intake, increased loss, increased demand, or a condition or disease that decreases the body’s ability to digest and absorb nutrients from available food. While the need for adequate nutrition is a constant, the demands of the body will vary, both on a daily and yearly basis.

  • During infancy, adolescence, and pregnancy additional nutrition is crucial for normal growth and development. A severe shortage of food will lead to a condition in children called marasmus that is characterised by a thin body and stunted growth. If enough calories are given, but the food is lacking in protein, a child may develop kwashiorkor – a condition characterised by oedema (fluid retention), an enlarged liver, apathy, and delayed development. Deficiencies of specific vitamins can affect bone and tissue formation. A lack of vitamin D, for instance, can affect bone formation – causing rickets in children and osteomalacia in adults, while a deficiency in folic acid during pregnancy can cause birth defects.
  • Acute conditions such as surgery, severe burns, infections, and trauma can drastically increase short-term nutritional requirements. People who have been malnourished for some time may have under functioning immune system and a poorer prognosis. They frequently take longer to recover from surgical procedures and spend longer in hospital. Malnutrition is common in patients admitted to hospital but it is easily overlooked by hospital staff. For this reason, many hospitals screen and monitor the nutritional status of their patients. This approach is recommended by the National Institute for Health and Care Excellence (NICE). Patients having surgery are frequently evaluated both prior to surgery and during their recovery process.
  • Chronic diseases may be associated with nutrient loss, increased nutrient demand, and with malabsorption (the inability of the body to absorb one or more available nutrients). Malabsorption may occur with chronic diseases such as coeliac disease, cystic fibrosis, pancreatic insufficiency, and pernicious anaemia. An increased loss of nutrients occur in chronic kidney disease, diarrhoea, and haemorrhaging. Sometimes conditions and their treatments can both cause malnutrition through decreased intake. Examples of this are the decreased appetite, difficulty swallowing, and nausea associated both with cancer (and chemotherapy), and with HIV/AIDS (and its drug therapies). Increased loss, malabsorption, and decreased intake may also occur in patients who chronically abuse drugs and/or alcohol.
  • Elderly patients are often less able to absorb nutrients due in part to decreased stomach acid production and are more likely to have one or more chronic ailments that may affect their nutritional status. At the same time, they may have more difficulty preparing meals and may have less access to a variety of nutritious foods. Older patients also frequently eat less due to a decreased appetite, decreased sense of smell, and/or mechanical difficulties with chewing or swallowing. For these reasons, elderly patients are more at risk of malnutrition and the requirement for nutritional support.
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About Malnutrition
  • 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, including:

    • Anaemia
    • Weight loss, decreased muscle mass, and weakness
    • Dry scaly skin
    • Oedema (swelling of limbs, due to build-up of fluid)
    • Hair that has lost its pigment
    • Brittle and malformed (spooned) nails
    • Chronic diarrhoea
    • Slow wound healing
    • Bone and joint pain
    • Growth retardation (in children)
    • Mental changes such as confusion and irritability
    • Goitre (enlarged thyroid gland)

    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 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. 


  • Tests

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

    If there are signs of malnutrition, the doctor may request general laboratory screening tests to evaluate a patient’s blood cells and organ function. Additional individual tests may be requested to look for specific vitamin and mineral deficiencies. If general malnutrition and/or specific deficiencies are diagnosed, then laboratory testing may be used to monitor the response to therapy. 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 should have their nutritional status assessed at the time of admission. This is usually done using a nutritional screening tool such as the MUST (Malnutrition universal screening tool) which involves assessing the patient’s body mass index (BMI), recent weight loss and presence of acute illness. If screening suggests that the individual is malnourished or at risk of developing malnourishment they should have a more detailed nutritional assessment which may include dietetic assessment and laboratory tests. If the results of these tests indicate possible nutritional deficits, patients may be provided nutritional support prior to a surgery or procedure and be monitored regularly during recovery. Nutritional support encompasses oral nutritional support (providing nutritional supplements to be taken by mouth), enteral nutrition (feeding through a tube directly into the gut) and parenteral nutrition (feeding into a vein).

    Laboratory tests may include:

    For general screening and monitoring:

    For nutritional status and deficiencies:

    • Prealbumin (is decreased in malnutrition and in acute illness. It’s level in the blood rises and falls rapidly in response to changes in nutritional status and can be used to detect short-term response to treatment). This test is not routinely performed in the UK.
    • Iron tests (such as Iron, TIBC, and Ferritin)
    • Vitamin and minerals (such as vitamin B12 and folate, vitamin D, vitamin K, calcium, and magnesium)
    • Trace element levels such as copper, zinc, selenium and manganese

    The results of these laboratory tests should always be considered in clinical context because they can be influenced by many conditions other than malnutrition. Laboratory tests are not a substitute for clinical assessment by a health professional.

    Non-Laboratory Tests
    Imaging and radiographic scans may be requested 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 (Magnetic Resonance Imaging)


  • Treatments

    Treatment of under nutrition includes:

    • Restoring the nutrients that are missing, making nutrient-rich foods available and providing supplements for specific deficiencies. Formal nutritional support may be required i.e. oral nutritional supplements, enteral feeding or parenteral nutrition. In someone who is severely malnourished, this must be done slowly until the body has had time to adjust to the increased intake and then maintained at a higher than normal level until a normal or near normal weight has been restored. A condition known as refeeding syndrome is a potentially fatal shift in fluid and electrolytes that can occur in malnourished patients when nutrients are re-introduced too quickly. This can be avoided by identifying the people at risk by carrying out a detailed nutritional assessment before refeeding is started and taking into account various factors such as recent weight change over time, alcohol intake and social and psychological factors.
    • Regular monitoring of those patients who have chronic malabsorption disorders or protein- or nutrient-losing conditions. Once the deficiencies have been treated, it may be necessary to put a treatment plan into place to prevent the malnutrition from recurring.
    • Dealing with any social, psychological, educational, and financial issues that may be causing or exacerbating the malnutrition, such as access to nutritious food.