Refeeding syndrome is a life-threatening electrolyte disturbance that occurs when nutrition is reintroduced too rapidly in patients who have been chronically malnourished or have had prolonged starvation. During starvation, intracellular phosphate, potassium, and magnesium are depleted. When carbohydrate is reintroduced, the surge in insulin drives these electrolytes from the extracellular to the intracellular space, causing profound hypophosphataemia, hypokalaemia, and hypomagnesaemia. Hypophosphataemia is the hallmark of refeeding syndrome and can cause heart failure, respiratory failure, haemolytic anaemia, and rhabdomyolysis.

Risk factors for refeeding syndrome include BMI <18.5 kg/m2, unintentional weight loss >10% in the preceding 3–6 months, little or no nutritional intake for more than 5 days, alcohol dependency, and chronic malabsorptive conditions. High-risk patients should have nutrition introduced at no more than 10 kcal/kg/day, increasing over 4–7 days, with close monitoring of electrolytes (phosphate, potassium, magnesium) at least twice daily for the first week. Prophylactic thiamine (100 mg TDS or IV if not absorbing) must be given before any glucose or nutrition is started in at-risk patients.