Refeeding syndrome occurs when beginning to “refeed” a severely malnourished person.  Malnutrition may be due to famine, disease or anorexia nervosa. The syndrome is exacerbated by a sudden shift from burning fats and protein to burning carbohydrates, which causes a dramatic fall in serum electrolytes accompanied by sodium and water retention. The fluid and electrolyte imbalances can lead to life-threatening complications including heart failure, convulsions, coma, and death. To prevent the syndrome, refeeding should not be aggressive; rather, it should begin with a high-protein, low-carbohydrate, very low calorie-diet fed orally or by tube, and the calories should be increased very gradually while monitoring electrolytes and physical signs. You might be interested in reading this journal article, Clinical Issues Encountered in the Refeeding of the Patient with Anorexia Nervosa.