During prolonged starvation or severe undernutrition, the body depletes intracellular stores of phosphate, potassium, and magnesium while total body levels appear normal in blood tests (because these minerals move out of cells into the bloodstream). When feeding resumes and carbohydrate intake rises, insulin surges — driving these electrolytes back into cells rapidly. Blood levels can fall precipitously.
Hypophosphataemia (critically low blood phosphate) is the hallmark. Phosphate is essential for ATP (energy) production; severe depletion causes muscle weakness, respiratory failure, cardiac arrhythmias, and neurological complications. Deaths have been reported. Hypomagnesaemia and hypokalaemia compound the risk.
At-risk patients include those with: anorexia nervosa, cancer cachexia, chronic alcoholism, severe prolonged illness, or those who have been without nutrition for more than 5 days. Refeeding risk also arises in the post-operative setting if nutritional support is started aggressively after a period of nil-by-mouth.
Management follows NICE clinical guideline CG32: identify at-risk patients, correct electrolyte abnormalities before feeding, start enteral nutrition at no more than 5–10 kcal/kg/day and increase slowly over 4–7 days, monitor electrolytes and cardiac status closely, and supplement thiamine (B1) — which is also depleted and required for carbohydrate metabolism.
This is a clinical topic. Refeeding of severely malnourished patients must be managed by a clinical team including a registered dietitian and medical clinician.