Refeeding syndrome: phosphate, thiamine, and prevention in ICU

Also known as Refeeding syndrome · Refeeding hypophosphataemia · Nutrition reintroduction syndrome · RFS

Refeeding syndrome (RFS) = potentially fatal metabolic disturbances that occur when food is reintroduced to STARVED patients (anorexia, alcoholism, prolonged fasting, post-operative, ICU after prolonged NBM). PATHOPHYSIOLOGY: starvation - depleted intracellular electrolytes (phosphate, potassium, magnesium) + low insulin. REFEEDING (carbohydrate) - INSULIN surge - electrolytes shift INTO cells (phosphate for ATP, potassium, magnesium) - serum levels PLUMMET - hypophosphataemia, hypokalaemia, hypomagnesaemia, thiamine depletion (Wernicke), fluid retention and salt retention - organ dysfunction and cardiac arrhythmias (arrhythmias, heart failure, sudden cardiac arrest are the most fatal manifestations). CLINICAL: mostly within the first 72 hours of starting nutrition. PREVENTION (NICE CG32): risk-stratify (box 1: BMI under 16, weight loss over 15 percent in 3 to 6 months, little or no intake over 10 days, low baseline K, PO4 or Mg), thiamine 200 to 300 mg immediately before and during the first 10 days of feeding, start at maximum 10 kcal/kg/day (5 kcal/kg/day in extreme cases: BMI under 14 or negligible intake over 15 days), supplement potassium 2 to 4, phosphate 0.3 to 0.6 and magnesium 0.2 to 0.4 mmol/kg/day, monitor biochemistry and cardiac rhythm.

medium16 referencesUpdated 19 Aug 202618 min readSource-verified · Oct 2026

Checked against its sources on 14 Oct 2026

The one-line answer

Refeeding syndrome (RFS) is the potentially fatal metabolic response when food returns to the starved: insulin-driven shifts of phosphate, potassium and magnesium into cells, severe hypophosphataemia, hypokalaemia and hypomagnesaemia, thiamine depletion, fluid and salt retention, and organ dysfunction with cardiac arrhythmias — arrhythmias, heart failure and sudden cardiac arrest are the most fatal manifestations. It declares itself mostly within the first 72 hours of nutrition. Prevent it the NICE way: identify the high-risk patient (BMI under 16, weight loss over 15 percent, little or no intake over 10 days, low baseline electrolytes — or two milder criteria), give thiamine 200 to 300 mg immediately before and during the first 10 days of feeding, start at a maximum of 10 kcal/kg/day (only 5 in extreme cases — BMI under 14 or negligible intake beyond 15 days), supplement potassium (likely 2 to 4 mmol/kg/day), phosphate (likely 0.3 to 0.6) and magnesium (likely 0.2 IV, 0.4 oral) unless pre-feeding levels are high, and correct fluid and electrolyte imbalances as standard care.^[4]^[10]^[1]

Meet the patient

A man in his sixties with metastatic oesophageal cancer and weeks of minimal intake is started on a full-rate NG feed for malnutrition. Within 72 hours he becomes dyspnoeic and confused, with sinus tachycardia and a new prolonged QT — phosphate fallen into the severe stratum (0·32 mmol/L or below, the Doig stratification cut-off) with hypokalaemia and hypomagnesaemia: increased glucose with hypophosphataemia, hypokalaemia and hypomagnesaemia, thiamine depletion, fluid imbalance and salt retention, resulting in impaired organ function and cardiac arrhythmias.^[7]^[2]

The question that decides his survival is not "why is he confused" — it is "why did his phosphate fall within 72 hours of feeding?" Occurrence is mostly within the first 72 hours of starting nutritional therapy, and that single trajectory is refeeding syndrome until proven otherwise; the carbohydrate in the feed is the trigger you must slow.^[1]

References16Show

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