Definition and diagnosis of malnutrition in adults

Although malnutrition refers to both overnutrition and undernutrition, it is commonly used to describe undernutrition. In these guidelines, the word malnutrition is used to describe undernutrition.

Malnutrition is associated with a deficiency of energy, protein and other nutrients, resulting in weight loss and changes in body composition. This may be difficult to assess in patients with fluid retention (eg ascites, oedema).

Malnutrition is diagnosed by the presence of any of the following: National Institute for Clinical Excellence (NICE), 2006

• body mass index (BMI) less than 18.5 kg/m²
• loss of more than 10% of body weight within the last 6 months
• BMI less than 20 kg/m² and unintentional loss of more than 5% of body weight within the last 6 months.

Malnutrition in adults can be diagnosed using a validated assessment tool such as the Subjective Global Assessment (SGA) or the Global Leadership Initiative on Malnutrition (GLIM) criteria.

The SGA should be completed by a trained professional such as an accredited practising dietitian. The SGA takes into account a physical assessment of lean body mass and fat mass, so it is particularly useful for patients with fluid retention (eg ascites, oedema), in whom BMI may not reflect nutritional status and may mask a reduction in lean body mass.

The GLIM criteria can be completed by a healthcare professional such as a doctor, nurse or an accredited practising dietitian. The GLIM criteria takes into account phenotypic criteria (eg unintentional weight loss, low BMI, reduced muscle mass) and etiologic criteria (eg reduced food intake, reduced absorption of food or nutrients, degree of inflammation or disease burden). To diagnose malnutrition, at least one phenotypic criterion and one etiologic criterion must be presentCederholm, 2019.

Clinical consequences of malnutrition include reduced muscle strength; impaired immune response, wound healing, psychosocial function, and recovery from illness and surgery; and poorer clinical outcomes (eg increased mortality, longer length of hospital stay, increased readmission rates).