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Gastroenterology & Nutrition

Malnutrition

Malnutrition (undernutrition) is inadequate intake, absorption or use of energy, protein or micronutrients that impairs function and clinical outcomes; identify it with validated screening, find the cause and provide safe, individualised nutrition support.

In a nutshell

Malnutrition is adult undernutrition that impairs function and recovery. Screen with MUST, then assess intake, weight trajectory, function, swallowing, cause and refeeding risk. Use food-first/oral support when safe, enteral feeding when oral intake is unsafe/inadequate but the gut works, and parenteral nutrition for appropriate gut failure. High-risk refeeding requires cautious calories, thiamine, electrolyte/fluid planning and close monitoring.

Classic presentation

An older inpatient has lost weight, eats little and is weak; MUST identifies high risk, while dysphagia and low phosphate make feeding route and refeeding safety urgent.

Key points

  • MUST uses BMI, unplanned weight loss and acute-disease effect; it is screening, not a complete nutritional assessment.
  • NICE considers nutrition support for BMI below 18.5, weight loss above 10%, BMI below 20 with weight loss above 5%, prolonged poor intake, malabsorption, losses or increased requirements.
  • Treat barriers and use food-first/oral support when swallowing is safe.
  • Enteral feeding needs inadequate/unsafe oral intake plus a functional, accessible gastrointestinal tract; consider gastrostomy when feeding is likely to last 4 weeks or more.
  • Parenteral nutrition is for inadequate/unsafe oral or enteral intake with a non-functional, inaccessible or leaking gut, under specialist oversight.
  • High-risk refeeding: NICE maximum 10 kcal/kg/day, 5 kcal/kg/day in extreme cases, with thiamine/vitamins, electrolyte planning and close monitoring.
  • Albumin is not a standalone nutritional marker; investigate the cause and follow the patient across care settings.

First-line investigation

MUST plus dietary/functional/swallowing assessment, weight trajectory and targeted blood tests including phosphate, magnesium, potassium, renal function and glucose.

Management

Identify high-risk feeding situations

  • Check airway/swallowing safety, fluid status, baseline phosphate/potassium/magnesium and NICE refeeding-risk criteria before starting substantial nutrition support; involve the specialist team early.1,6

Screen and assess the cause

  • Calculate MUST, document intake and weight trajectory, assess function and social barriers, and investigate dysphagia, malabsorption, chronic disease, malignancy, medication, dental and psychological causes.2,4,1

Optimise food-first and oral nutrition

  • Treat reversible symptoms and provide assistance, fortified food, snacks, altered meal patterns and balanced oral supplements when swallowing is safe; involve dietetics and carers.1,5,8

Escalate to enteral feeding when the gut works

  • Use enteral feeding for inadequate or unsafe oral intake with a functional, accessible gut; use the appropriate gastric/post-pyloric route and consider gastrostomy for likely feeding of 4 weeks or more.1

Use specialist parenteral nutrition for gut failure

  • Consider parenteral nutrition when oral/enteral intake is inadequate or unsafe and the gut is non-functional, inaccessible or leaking; introduce progressively and monitor through the specialist nutrition team.1,9

Prevent refeeding and continue the plan

  • Use cautious energy initiation, thiamine/vitamins, electrolyte and fluid monitoring, regular review and cross-setting handover; reassess route, goals, tolerance, weight, function and the underlying cause.1,7,6

Exam traps

  • MUST is a risk screen and does not replace dietetic, swallowing or cause assessment.
  • Normal pre-feeding phosphate, potassium or magnesium does not exclude total-body depletion and refeeding risk.
  • Do not delay all feeding until every electrolyte is normal; use the specialist refeeding protocol and replace/monitor alongside feeding.
  • Use the gut if it is functional and accessible; parenteral nutrition is not a routine substitute for oral or enteral support.
  • A normal albumin does not rule out malnutrition because albumin changes with inflammation and illness.
  • Dysphagia needs trained swallowing assessment; modified texture is not automatically safe without review.
  • Do not use general adult calorie targets for extreme malnutrition or specialist eating-disorder pathways.

Illustrations

Clinical manifestations of severe childhood malnutritionA clearly labelled paediatric clinical photograph showing severe protein-energy malnutrition and wasting. Use only as a visual example of phenotype, with adult nutrition-support guidance kept separate.CDC, Wikimedia Commons · Public domain

Key sources

  1. NICE CG32, Nutrition support for adults: oral nutrition support, enteral tube feeding and parenteral nutrition (Published 22 February 2006; last updated 4 August 2017)Updated 4 Aug 2017
  2. BAPEN Malnutrition Universal Screening Tool (MUST) (Current MUST tool and five-step adult screening/management pathway)
  3. NHS, Malnutrition (Adult undernutrition signs, causes, risk factors and initial treatment)Updated 23 May 2023
  4. BAPEN, Nutritional assessment (Assessment of intake, anthropometry, disease state, function and targeted biochemical interpretation)
  5. NHS, Malnutrition: treatment (Oral, enteral and community nutrition-support information)
  6. BAPEN/BSG Position Statement on Electrolyte and Vitamin Replacement in Adult Patients with Severe Malnutrition (Updated 16 July 2026; severe malnutrition and refeeding electrolyte, vitamin and fluid safety)Updated 16 Jul 2026
  7. NICE QS24, Nutrition support in adults (Quality standard supporting screening, treatment and coordinated nutrition support)
  8. NHS England, National standards for healthcare food and drink (Screening, assisted mealtimes and food-first care in healthcare settings)
  9. BAPEN/BSG position statements on intestinal failure (Specialist UK guidance for patients requiring parenteral support)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.