Refeeding syndrome: It is a disorder of electrolyte metabolism characterized by hypophosphatemia and a series of symptoms resulting from the reintroduction of nutrients after prolonged starvation or malnutrition. The pathological mechanism of the re-feeding syndrome is the rapid transfer of phosphorus into cells for phosphorylation in the process of sugar and protein synthesis, resulting in a decrease in blood phosphorus, which causes myocardial dysfunction and neurological complications and a series of resulting symptoms. Hypophosphatemia is the main pathophysiological feature of RFS, hypokalemia is the main cause of death in RFS, along with hypomagnesemia, vitamin B1 deficiency and other manifestations. From this point of view, it is advisable to hospitalize patients with anorexia nervosa who are underweight to gain weight, and plasma phosphorus levels need to be tested during the first few days of re-feeding. As soon as a decrease in blood phosphorus is detected, it should be supplemented by oral methods.