Patients with severe malnutrition may have a deficit of total body phosphate. Introduction of feeds can result in refeeding syndrome, characterized by life-threatening hypophosphatemia. Phosphate levels should be closely monitored and maintained during initial phases of refeeding.

The majority of the body’s phosphate is stored in the form of adenosine triphosphate (ATP). Because phosphates are ubiquitous in foods, total body phosphate depletion occurs only in cases of severe malnutrition. Patients with severe malnutrition are more than 30% to 35% less than ideal body weight. In the pediatric population in the United States, anorexia nervosa and bulimia nervosa represent a large percentage of these cases. Children with chronic disease and those who are neglected or abused may also be affected.

Refeeding syndrome occurs because of rapid refeeding in a severely malnourished patient. Intravenous or enteral administration of carbohydrate stimulates insulin release by the pancreas, resulting in increased cellular uptake of glucose and phosphate, particularly in the liver and skeletal muscle. This acute shift of phosphate from the extracellular to the intracellular compartment in a patient with total body phosphate depletion results in acute hypophosphatemia. Refeeding syndrome can also cause hypoglycemia, hypokalemia, and hypomagnesemia by a similar mechanism. Fluid overload, edema, and gastrointestinal dysmotility also occur.