what is malnutrition
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What is malnutrition?

Malnutrition affects people affects people of all ages and income levels. In this article we explore what is malnutrition, what are the factors that affect it, how to assess malnutrition and how to address malnutrition.

What is malnutrition?

“Malnutrition refers to deficiencies, excesses or imbalances in a person’s intake of energy and/or nutrients. The term malnutrition covers 2 broad groups of conditions. One is ‘undernutrition’-which includes stunting (low height for age), wasting (low weight for height), underweight (low weight for age) and micronutrient deficiencies or insufficiencies (a lack of important vitamins and minerals). The other is overweight, obesity and diet-related noncommunicable diseases (such as heart disease, stroke, diabetes, and cancer)” (1).

In addition to the definition above, the physical manifestations of malnutrition include low birthweight (2), low height or BMI in adulthood (2), weight loss, muscle loss and subcutaneous fat loss (3).

Malnutrition is associated with a weakened immune system (4, 5, 6), poor wound healing (5) and respiratory function (4, 5). In hospitalized patients, malnutrition is associated with increased risk of infection (4), increased length of stay and higher mortality rates (4, 5). In older age, malnutrition represents an increased risk for sarcopenia, osteoporosis, frailty, falls, fractures, infection and mortality, as well as decreased quality of life (6, 7).

Malnutrition can happen at any stage of life, however it is more prevalent in hospitalised patients (5), individuals over 65 years of age, particularly those living in aged care facilities (5, 6, 7) and individuals with chronic health conditions (5). Malnutrition is particularly concerning in the context of life-threatening diseases such as cancer (3). Unfortunately, malnutrition is often underdiagnosed and, therefore, untreated, in part due to lack of standardised protocols (5).

Factors that affect malnutrition

  • Gut health: malnutrition can be associated with dysbiosis (2). Conversely, the combination of obesity and dysbiosis leads to higher risk of chronic health conditions and inflammation (2).
  • Mother’s nutritional status: if the mother is undernourished, the child is at increased risk of low weight/height and micronutrient deficiencies. Small weight at birth is often correlated with obesity later in life in affluent countries. These children are at increased of developing chronic health conditions later in life. On the other hand, maternal obesity is associated with nutrient deficiencies, which also impact the development of the child (2).
  • Ethnicity: indigenous and ethnic minorities tend to have lower birth weight and childhood undernutrition, particularly in affluent countries (2).
  • Urbanisation level: rural populations have higher prevalence of low height in childhood (2).
  • Physiological factors in older adults: including decreased appetite (6, 7, 8) due to slower gastrointestinal transit and changes in satiety hormones (7), dysphagia (i.e. difficulty swallowing) and poor dentition (6, 8).
  • Psychosocial factors in older adults: including dementia, depression (6, 8) and cognitive impairment (8).
  • Physical function in older adults: older adults who are unable to perform activities of daily living without assistance are at greater risk of malnutrition (8).

Assessing malnutrition

Screening tools

The tools used in different countries and settings for the screening of malnutrition include:

  • Mini Nutritional Assessment (MNA): jointly developed by the Center for Internal Medicine and Clinical Gerontology, the Clinical Nutrition Program at the University of New Mexico and the Nestlé Research Center. It is widely used in geriatric patients in hospitals and aged care facilities (5, 6)
  • Mini Nutritional Assessment Short Form (MNA-SF): appropriate for older adults (5, 6)
  • Malnutrition Universal Screening Tool (MUST): developed by the British Association for Parenteral and Enteral Nutrition, common in Australia and used in all types of hospitalised patients (3, 5, 6)
  • Malnutrition Screening Tool (MST): developed in 1999 by Ferguson et al., common in Australia and recommended for patients in hospitals, aged care facilities and outpatients (i.e. those receiving treatment in a clinic) (3, 5)
  • Malnutrition Screening Tool for Cancer Patients (MSTC) (3)
  • Subjective Global Assessment (SGA): developed by Detsky et al., in 1987, it is commonly used in cancer patients (5, 6)
  • Patient-Generated Subjective Global Assessment Short Form (PG-SGA SF): commonly used in cancer patients (3, 5)
  • Simplified Nutritional Appetite Questionnaire (SNAQ): developed in the Netherlands (5)
  • Nutritional Risk Screening 2002 (NRS 2002): developed from 128 studies (5, 6)
  • Nutrition Risk in the Critically Ill (NUTRIC Score): developed by Heyland et al., in 2011, recommended for patients in critical care (5)
  • ESPEN Criteria: developed by the European Society for Clinical Nutrition and Metabolism (ESPEN) (5)
  • AND/ASPEN Tool (ASPEN): developed by the American Society for Parenteral and Enteral Nutrition (ASPEN), similar to the SGA (5)

Nutritional assessment

Nutrition status

Nutrient deficiencies can be measured by depleted stores or circulating concentrations (2). The biomarkers that seem to correlate best with screening tools are albumin, haemoglobin, total cholesterol, prealbumin and total protein (9).

Addressing malnutrition

Nutrient requirements

Energy intake

  • 105-125 kJ/kg/day for cancer patients (3)
  • lower requirements for older individuals (7)

Protein intake

  • 1.0-1.5 kg g/kg/day for cancer patients (3)
  • 1.0-1.2 kg/g/day for healthy older individuals (6, 7)
  • 1.2-1.5 kg/d/day for older individuals at risk of malnutrition or with malnutrition including those with chronic disease or acute injury (6, 7)
  • up to 2.0 kg/d/day for older individuals with severe malnutrition (6)


  • Calcium and vitamin D: older individuals should ensure adequate intake to minimise boned mineral density loss and fractures and account for decreased vitamin D synthesis (7).
  • B vitamins: older individuals should ensure adequate intake of vitamins B12, B6 and folic acid due to impaired absorption (7).


Oral nutritional supplements (ONS)

ONS are commonly indicated for older individuals to increase energy, protein and micronutrient intake without necessarily increasing fullness. In addition, there is evidence that ONS can increase anthropometric measures such as weight, BMI and upper arm circumference (6).

Food fortification

Fortifying foods with extra protein and energy can increase protein and energy intake without necessarily affecting satiety (6, 7). Common ways of food fortification include adding dairy products (e.g. cream, butter) to meals and using protein-enriched meals such as breads, soups and snacks (6).

Enteral and parenteral nutrition

Enteral nutrition (i.e. tube feeding) and parenteral nutrition (i.e. intravenous nutrition) might be required for certain types of cancers such as head and neck and gastrointestinal (3).


  • Resistance exercise: important for preventing muscle loss (3).
  • Aerobic exercise: important for cardiovascular health, insulin sensitivity and managing inflammation (3).


Some drugs may be used to combat malnutrition include those that improve anabolism (muscle growth) or appetite (3).

Food characteristics

  • Palatability: increasing the palatability of food (e.g. by using MSG) can but not always increase food intake in older malnourished individuals (7).
  • Variety: variety within a meal can also but not always increase food intake in older malnourished individuals (7).
  • Texture: liquid foods tend to be less filling, facilitating intake (7).
  • Packaging: packaging that is easy to open and have labels that are easy to read are important for older malnourished individuals (7).

Social eating

Eating with other people is important for older individuals, as it can increase food intake (7).

Meal delivery services

Meal delivery services such as Meals on Wheels can facilitate food intake in older individuals who can’t or are not motivated to cook for themselves (7).

Food preparation skills

Older individuals who are able to cook should be encourage to do so, as this can stimulate appetite and interest in food (7).


  • Organization WH. Malnutrition [Internet]. [cited 2022 Oct 9]. Available from: https://www.who.int/news-room/questions-and-answers/item/malnutrition
  • Wells JC, Sawaya AL, Wibaek R, Mwangome M, Poullas MS, Yajnik CS, et al. The double burden of malnutrition: aetiological pathways and consequences for health. Lancet (London, England). 2020 Jan;395(10217):75–88.
  • Kiss N, Loeliger J, Findlay M, Isenring E, Baguley BJ, Boltong A, et al. Clinical Oncology Society of Australia: Position statement on cancer-related malnutrition and sarcopenia. Nutr Diet. 2020 Sep;77(4):416–25.
  • Ponce J, Anzalone AJ, Bailey K, Sayles H, Timmerman M, Jackson M, et al. Impact of malnutrition on clinical outcomes in patients diagnosed with COVID-19. J Parenter Enter Nutr [Internet]. 2022 Jun 7;n/a(n/a). Available from: https://doi.org/10.1002/jpen.2418
  • Serón-Arbeloa C, Labarta-Monzón L, Puzo-Foncillas J, Mallor-Bonet T, Lafita-López A, Bueno-Vidales N, et al. Malnutrition Screening and Assessment. Nutrients. 2022 Jun;14(12).
  • Mathewson SL, Azevedo PS, Gordon AL, Phillips BE, Greig CA. Overcoming protein-energy malnutrition in older adults in the residential care setting: A narrative review of causes and interventions. Ageing Res Rev. 2021 Sep;70:101401.
  • Clegg ME, Williams EA. Optimizing nutrition in older people. Maturitas. 2018 Jun;112:34–8.
  • O’Keeffe M, Kelly M, O’Herlihy E, O’Toole PW, Kearney PM, Timmons S, et al. Potentially modifiable determinants of malnutrition in older adults: A systematic review. Clin Nutr. 2019 Dec;38(6):2477–98.
  • Zhang Z, Pereira SL, Luo M, Matheson EM. Evaluation of Blood Biomarkers Associated with Risk of Malnutrition in Older Adults: A Systematic Review and Meta-Analysis. Nutrients. 2017 Aug;9(8).

[Photo by Alex Boyd on Unsplash]

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