PassFinals
Endocrinology & Metabolic

Refeeding syndrome

Refeeding syndrome is a potentially fatal metabolic and fluid complication of restarting nutrition in a severely malnourished or starved person; insulin shifts phosphate, potassium and magnesium into cells, while carbohydrate use can expose thiamine deficiency and sodium-water retention can cause fluid overload.

In a nutshell

Refeeding syndrome is a potentially fatal electrolyte and fluid shift after restarting nutrition in a severely malnourished or starved person. Falling phosphate is the classic early signal; potassium and magnesium can also fall, thiamine deficiency can cause Wernicke encephalopathy and sodium-water retention can cause oedema or cardiac failure. Identify risk before feeding, give thiamine and vitamins, start the general adult high-risk pathway at no more than 10 kcal/kg/day (5 in extreme risk), replace electrolytes and monitor closely.

Classic presentation

A person with anorexia nervosa, alcohol dependence or prolonged poor intake whose phosphate, potassium or magnesium falls and who becomes weak, oedematous, breathless, arrhythmic or confused within the first few days of feeding.

Key points

  • Normal pre-feeding electrolytes do not exclude severe intracellular depletion.
  • The classic biochemical warning is a new fall in phosphate after feeding, often with potassium and magnesium depletion.
  • Give thiamine and vitamins before or with the first calories; oral/enteral thiamine is preferred when feasible.
  • For general high-risk adult medical malnutrition, start at a maximum of 10 kcal/kg/day; use 5 kcal/kg/day with continuous cardiac monitoring in extreme risk.
  • Replace potassium, phosphate and magnesium proactively, avoid sodium/fluid overload and do not allow fear of refeeding to cause prolonged underfeeding.
  • Higher-calorie eating-disorder refeeding is a specialist MEED pathway, not a universal replacement for NICE CG32.

First-line investigation

Baseline and serial phosphate, potassium, magnesium, adjusted calcium, renal function, glucose, fluid balance and ECG/cardiac assessment according to risk.

Management

Identify risk before feeding

  • Use NICE CG32 criteria, assess acute illness and arrange nutrition-team oversight; extreme risk or instability may require HDU/critical-care capability.1,2

Thiamine, vitamins and baseline tests

  • Give thiamine and a balanced vitamin preparation before or with the first calories, and measure phosphate, potassium, magnesium, calcium, renal function and glucose before feeding.1,4,2

Start nutrition cautiously

  • For general high-risk adult medical malnutrition start at no more than 10 kcal/kg/day; use 5 kcal/kg/day in extreme risk and increase to full needs over 4 to 7 days under supervision.1,2

Replace electrolytes and control fluid

  • Replace potassium, phosphate and magnesium proactively unless levels are high, and prescribe fluid and sodium according to volume status, losses and renal/cardiac risk.1,2,5,6

Treat deterioration as an emergency

  • For severe electrolyte falls, arrhythmia, cardiac or respiratory failure, fluid overload or neurological signs, stop calorie escalation or reduce to the last tolerated rate, replace deficits urgently and seek senior nutrition/critical-care advice.2,3

Continue surveillance

  • Monitor at least daily until stable, more often when high risk or unstable, and arrange follow-up because late refeeding problems can occur in severe malnutrition.1,2,3

Exam traps

  • Normal serum phosphate before feeding does not reassure because total-body stores may be depleted.
  • Do not give carbohydrate to a thiamine-depleted patient without first addressing thiamine risk.
  • Hypophosphataemia is the classic signal, but refeeding syndrome also involves potassium, magnesium, thiamine and fluid shifts.
  • Do not automatically stop all nutrition: stop escalation or reduce the rate, replace deficits and escalate urgently when clinically significant deterioration occurs.
  • Do not apply MEED's specialist eating-disorder calorie pathway to a medically unstable adult with general malnutrition.

Key sources

  1. NICE CG32: Nutrition support for adults: oral nutrition support, enteral tube feeding and parenteral nutrition (Current NICE adult nutrition-support guideline; published 2006 and last updated 4 August 2017. Provides refeeding-risk criteria, 10/5 kcal/kg/day starting rates, 4-to-7-day advancement and monitoring recommendations.)Updated 4 Aug 2017
  2. BAPEN/BSG: Position Statement on Electrolyte and Vitamin Replacement in Adult Patients with Severe Malnutrition (Updated July 2026; current UK position statement on electrolyte and vitamin replacement, fluid and sodium exposure, monitoring, IV access and refeeding-related escalation.)Updated 16 Jul 2026
  3. Royal College of Psychiatrists CR233: Medical Emergencies in Eating Disorders (MEED) (May 2022 guidance, superseding MARSIPAN reports; eating-disorder-specific risk, refeeding, monitoring, escalation and underfeeding guidance. Use within specialist eating-disorder and acute-medical pathways.)Updated 1 Oct 2023
  4. NHS Specialist Pharmacy Service: Prescribing and using thiamine to prevent refeeding syndrome (Published 2 May 2024 and last updated 11 March 2025; current UK medicines advice prioritising oral/enteral thiamine and reserving IV thiamine for when the oral or enteral route is unavailable.)Updated 11 Mar 2025
  5. NICE CG174: Intravenous fluid therapy in adults in hospital (NICE fluid-prescribing and monitoring principles relevant to malnutrition, fluid overload, renal impairment and cardiac failure; accessed 4 August 2026.)
  6. British National Formulary (BNF) (Current UK prescribing information for thiamine, vitamin preparations, phosphate, potassium and magnesium; product-specific doses, routes, contraindications, interactions and monitoring must be checked at the point of prescribing; accessed 4 August 2026.)

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.