Malnutrition | Definition | Clinical Features

Malnutrition refers to a sudden or chronic decrease in the intake of sufficient nutrition to support the body’s requirements for growth, healing, and maintenance of life. Malnutrition can be acute or chronic:

Acute malnutrition: a brief period of inadequate nutrition that is most commonly in relation to an acute illness with a high inflammatory state, such as pneumonia, and results in muscle wasting and rapid weight loss.
Chronic malnutrition: inadequate nutrition that lasts longer than three months. Often secondary to social, behavioural, and economic factors in addition to illness-related causes.

It is estimated that over 30% of patients admitted to hospital will experience a form of malnutrition.1,2
All patients admitted to hospital should be screened for malnutrition including measurement of their weight, body mass index (BMI) and appetite. Several standardised screening tools exist including the Malnutrition Universal Screening Tool (MUST), the Malnutrition Screening Tool (MST) and Mini-Nutrition Assessment (MNA).4
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Normally, as metabolic demands increase due to illness, injury or stressors such as exercise, people are able to adapt their nutritional intake to meet their body’s requirements.
In settings of chronic disease and certain drugs, this can become extremely difficult and lead to acute or chronic malnutrition. 
There are three main reasons why someone might become malnourished:

Inadequate amounts of nutrients (e.g. poor variety in diet)
Difficulty absorbing nutrients (e.g. gastrointestinal dysfunction such as coeliac disease)
Increased nutritional demands (e.g. post-surgery for healing)

Risk factors
Those most at risk of malnutrition are patients with chronic illnesses, the elderly, those living in supported accommodation and patients drinking excessive amounts of alcohol over a prolonged period.
Other risk factors for malnutrition include:

Being hospitalised for extended periods of time
Problems with dentition, taste or smell
Social isolation and loneliness
Mental health issues including grief, anxiety and depression
Cognitive issues including confusion

Clinical features
A comprehensive nutrition-focused history and exam should occur to evaluate the cause and severity of the malnutrition and determine an appropriate management plan. 
Typical clinical features of malnutrition include:3

High susceptibility or long durations of infections
Slow or poor wound healing
Altered vital signs including bradycardia, hypotension, and hypothermia
Depleted subcutaneous fat stores
Low skeletal muscle mass

In children, other indicators of undernutrition include:

Wasting: low weight for height
Stunting: low height for age
Underweight: low weight for age

Serum albumin
Hypoalbuminaemia occurs in conditions where there is an excessive amount of protein being lost (e.g. protein-losing enteropathy, chronic renal disease) or where the production of albumin is impaired (e.g. liver disease due to loss of synthetic function or malnutrition due to a paucity of protein). Hypoalbuminaemia can also develop in the context of inflammatory states such as infections. As a result, serum albumin should not be relied on in isolation to assess a patient’s nutritional state as there are a wide variety of factors which influence levels.

Important areas to cover in the history include:

Weight history: including current weight, recent changes to weight and changes to fit of clothes
Meal history: regularity of meals including skipping meals
Protein intake: intake of high-quality protein
Hydration: intake of fluids

Clinical examination
Clinical examination of a patient with suspected malnutrition should include:

Weight: unexpected weight loss from someone’s normal weight is indicative of a period of malnutrition. This includes people who are clinically overweight and obese.
Body mass index (BMI): a patient’s BMI indicates whether they might be malnourished. It is not however as accurate as history and clinical examination, and should never be used in isolation.
Review of muscle mass stores
Review of subcutaneous fat stores

Consideration could also be given to measuring a patient’s grip strength, triceps skin fold thickness and mid-arm muscle circumference.5

Malnutrition should be treated like any other medical condition with consideration of the patient’s goals of care, prognosis, and other social factors. Dietitians should be involved in leading the management of patients with malnutrition.
If a specific reversible cause of malnutrition is identified (e.g. infection or inflammatory state), this should be treated as soon as possible.
Method of feeding2
Oral nutrition should be used as long as it is possible, with the use of oral nutritional support such as high-energy-high-protein supplements and fortified food products. Often, minor changes to diet will have a significant positive impact on a patient’s nutritional status. 
If a patient is unable to safely swallow or is unable to take sufficient calories orally, nasogastric feeding should be considered. For long-term feeding, a gastrostomy (PEG or RIG) or jejunostomy should be considered.
Parenteral nutrition should be reserved for patients with intestinal failure or inaccessible digestive tracts.

Refeeding syndrome7
Refeeding syndrome is a condition caused by a rapid re-introduction of normal nutrition in patients who are chronically malnourished. In the context of chronic malnutrition, a patient’s intracellular stores of key electrolytes such as potassium and phosphate become depleted. As a result, if a patient is suddenly provided with normal levels of nutrition, there is a sudden shift of these electrolytes from the extracellular to the intracellular compartment driven by a large insulin response and other factors. This can ultimately lead to a sudden drop in extracellular levels of key electrolytes resulting in hypokalaemia and hypophosphataemia. This can subsequently lead to cardiac complications (e.g. arrhythmias) and seizures.
To prevent refeeding syndrome, nutrition is re-introduced more gradually under the guidance of a dietician and the patient’s electrolytes are monitored closely, allowing deficiencies to be identified early and replaced appropriately.

Complications of malnutrition include:

Impaired immunity (increased risk of infections)
Poor wound healing
Growth restriction in children
Unintentional weight loss, specifically the loss of muscle mass
Multi-organ failure

Key points

Malnutrition refers to a sudden or chronic decrease in the intake of sufficient nutrition to support the body’s requirements for growth, healing, and maintenance of life. It can be acute or chronic. 
Validated screening tools for malnutrition include MUST, MST and MNA.
Major risk factors include chronic illness, increasing age, living in supported accommodation and alcohol abuse. 
A comprehensive nutrition-focused history and exam are required to assess the cause and severity of the malnutrition and determine an appropriate management plan. 
When treating malnutrition, it is important to always consider oral methods of nutritional support first before opting for parenteral routes.
Complications of malnutrition include increased risk of infections, poor wound healing, growth restriction (in children), loss of muscle mass and organ failure/death.

Dr Chris Jefferies


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Stewart R. Handbook of clinical nutrition and dietetics. Sixth edition. ed: Australian Dietitian; 2020.
Validated Malnutrition Screening and Assessment Tools: Comparison Guide. 2022. Available from: [LINK]
Hummell A, Cummings M. Role of the nutrition‐focused physical examination in identifying malnutrition and its effectiveness. Nutrition in Clinical Practice. 2021;37(1):41-49. Available from: [LINK]
Bretscher C, Boesiger F, Kaegi-Braun N, Hersberger L, Lobo D, Evans D et al. Admission serum albumin concentrations and response to nutritional therapy in hospitalised patients at malnutrition risk: Secondary analysis of a randomised clinical trial. eClinicalMedicine. 2022;45:101301.
Nickson C. Refeeding Syndrome. Life in the Fast Lane. 2022. Available from: [LINK]