The parallels to CFS and refeeding syndrome are striking, body using mostly protein/fat for energy (ketones) and low potassium, magnesium, phosphorous and B1... http://en.wikipedia.org/wiki/Refeeding_syndrome Any individual who has had negligible nutrient intake for more than 5 consecutive days is at risk of refeeding syndrome. Refeeding syndrome usually occurs within four days of starting to feed. Patients can develop fluid and electrolytedisorders, especially hypophosphatemia, along with neurologic, pulmonary, cardiac, neuromuscular, and hematologic complications. During prolonged fasting the body aims to conserve muscle and protein breakdown by switching to ketone bodies derived from fatty acids as the main energy source. The liver decreases its rate of gluconeogenesis thus conserving muscle and protein. Many intracellular minerals become severely depleted during this period, although serum levels remain normal. Importantly, insulin secretion is suppressed in this fasted state and glucagon secretion is increased. During refeeding, insulin secretion resumes in response to increased blood sugar; resulting in increased glycogen, fat and protein synthesis. This process requires phosphates, magnesium and potassium which are already depleted and the stores rapidly become used up. Formation of phosphorylated carbohydrate compounds in the liver and skeletal muscle depletes intracellular ATP and 2,3-diphosphoglycerate in red blood cells, leading to cellular dysfunction and inadequate oxygen delivery to the body's organs. Refeeding increases the basal metabolic rate. Intracellular movement of electrolytes occurs along with a fall in the serum electrolytes, including phosphate, potassium and magnesium.Glucose, and levels of the B vitamin thiamine may also fall. Cardiac arrhythmias are the most common cause of death from refeeding syndrome, with other significant risks including confusion, coma and convulsions and cardiac failure. This syndrome can occur at the beginning of treatment for anorexia nervosa when patients are reintroduced to a healthy diet. The shifting of electrolytes and fluid balance increases cardiac workload and heart rate. This can lead to acute heart failure. Oxygen consumption is also increased which strains the respiratory system and can make weaning from ventilation more difficult.