Pathophysiology
Clinical meaning
Refeeding syndrome is a potentially fatal metabolic complication that occurs when nutritional intake is reintroduced after a prolonged period of starvation or severe malnutrition (as in anorexia nervosa, chronic alcoholism, prolonged fasting, or cancer cachexia). During starvation, the body shifts from carbohydrate metabolism to fat and protein catabolism; intracellular stores of phosphate, potassium, and magnesium become depleted as these electrolytes are excreted renally, though serum levels may appear normal due to extracellular redistribution. When carbohydrates are reintroduced, insulin secretion surges, driving glucose and electrolytes (particularly phosphate, potassium, and magnesium) from the extracellular space into cells for anabolic processes. This rapid intracellular shift causes precipitous drops in serum phosphate (hypophosphatemia -- the hallmark of refeeding syndrome), potassium, and magnesium. Hypophosphatemia impairs ATP production (affecting cardiac, respiratory, and skeletal muscle function), causes 2,3-DPG depletion (shifting the oxygen dissociation curve leftward, reducing tissue oxygen delivery), and produces rhabdomyolysis. Additionally, insulin-mediated sodium and water retention causes fluid overload, which can precipitate heart failure in a malnourished heart with reduced cardiac mass and contractility. The clinician identifies at-risk patients using NICE criteria, initiates nutrition cautiously...