AKT · Endocrine/Lipids, metabolic & inherited

Refeeding syndrome

Metabolic shifts on reintroducing nutrition after starvation (insulin surge → ↓PO4/K/Mg)

Overview

Potentially fatal fluid and electrolyte shifts when nutrition is reintroduced to a malnourished/starved person. Refeeding carbohydrate triggers insulin release, driving phosphate, potassium and magnesium intracellularly and depleting thiamine — causing HYPOPHOSPHATAEMIA, hypokalaemia, hypomagnesaemia, fluid overload, arrhythmia and Wernicke's. Prevented by identifying risk, starting low and slow, and replacing electrolytes + thiamine.

Recognise

Occurs within days of refeeding a starved patient (prolonged fasting, anorexia nervosa, alcohol dependence, post-bariatric, malabsorption)
HYPOPHOSPHATAEMIA (the hallmark), hypokalaemia, hypomagnesaemia; fluid retention/oedema
Consequences: cardiac arrhythmia/failure, respiratory failure, rhabdomyolysis, seizures, Wernicke's encephalopathy

Red flags

Severe hypophosphataemia → cardiac arrhythmia/respiratory failure → urgent replacement and slow feeding
High-risk patient (BMI very low, little intake for >10 days, low pre-feeding electrolytes) → NICE high-risk criteria

Differentials & how to tell them apart

Other causes of hypophosphataemiaDKA recovery, alcohol, hyperventilation — but the refeeding context is key

Sepsis / cardiac failureoverlapping deterioration — check electrolytes and the feeding timeline

Investigations

Baseline and daily phosphate, potassium, magnesium, calcium, glucose; identify NICE risk criteria before feeding.

Management

Identify risk → thiamine + cautious feeding + electrolyte (PO4/K/Mg) replacement

1Identify at-risk patients (NICE criteria) BEFORE feeding. Give thiamine, start feeding at reduced calories and increase slowly, and monitor + replace phosphate, potassium and magnesium daily.Gate: Give THIAMINE before/with the first carbohydrate (carbohydrate without thiamine precipitates Wernicke's); start LOW and SLOW — feeding a starved patient at full rate triggers the lethal phosphate/potassium shift
2Continue daily electrolyte monitoring and replacement; escalate feeding gradually; cardiac monitoring if severe.

Thiamine (BEFORE/with carbohydrate) — prevents Wernicke's — give before refeeding in at-risk patients

Phosphate, potassium, magnesium replacement — correct and monitor closely

Start feeding low and slow — reduced calories initially, increase gradually with monitoring

Key points

Reintroducing food to the starved → insulin surge → phosphate/potassium/magnesium crash + thiamine depletion. Prevent it: spot the risk, thiamine first, feed low and slow. Hypophosphataemia is the signature. Classic in anorexia nervosa and alcohol dependence.

Monitor & prognosis

Daily PO4/K/Mg/glucose; cardiac status.

Preventable; dangerous if unrecognised.

Source: NICE CG32 (nutrition support); MARSIPAN