This is an extremely important post for those recovering from a restrictive eating disorder, so please take notice of this, as many of those recovering from REDs are unaware of RFS.

A lot of the text below is taken from the MARSIPAN: Management of Really
Sick Patients with Anorexia Nervosa (October 2010). It is very wordy so I took the most relevant parts to bring to your attention, but you can click the link above for the entirety of the MARSIPAN Guidelines. The text from MARSIPAN is referenced as so.

Firstly, I am going to share with you a simplified version of what refeeding syndrome is and how to recognise it.

Refeeding syndrome symptoms may occur when a person receives a large intake of carbohydrates following a period of starvation.

A severe shift in electrolytes takes place when an individual consumes a quantity of complex carbohydrates after a prolonged period of food deprivation. This in turn, causes fluid imbalances in the body, leading to the potentially fatal conditions of hypophosphatemia and heart failure.

Hypophosphatemia refers to an abnormally low concentration of phosphates in the blood stream. This is linked to the transport and cellular uptake of phosphorus and potassium due to excess insulin secretion. Refeeding syndrome symptoms arise when the malnourished person no longer needs to utilize stored fat and protein, and instead metabolizes carbohydrates. The resulting rapid discharge of insulin causes the drop in serum phosphate, producing the clinical symptoms of refeeding syndrome.

Unfortunately, certain early signs of refeeding syndrome may go undetected as they are somewhat unspecific. However, symptoms such as generalized weakness, seizures, muscle fibre breakdown, white blood cell dysfunction, low blood pressure, respiratory failure, arrhythmias, cardiac arrest, and sudden death have all been documented as part of this serious and even fatal syndrome.

Refeeding syndrome symptoms can be of concern to those recovering from eating disorders such as anorexia, as they are at risk of developing hypophosphatemia when starting to eat again. Medical supervision and monitoring by nutritionists and other health professionals familiar with this condition can help improve the outcome for those individuals struggling to re-gain normal eating behavior. (from here)

Below I share information that goes into far more detail in regards to refeeding syndrome, taken from the MARSIPAN guidelines, and the online Nursing Centre – this is quite complex and detailed information regarding refeeding syndrome in a hospital setting.

Re-feeding syndrome is a potentially fatal condition (World Health Organization, 1999; Winston et al, 2000; Crook, 2001; Casiero & Frishman, 2006; Mehanna et al, 2008) that occurs when patients who have had their food severely restricted are given large amounts of food via oral or nasogastric re-feeding as well as during TPN. It has been noted in outpatients with anorexia nervosa who have suddenly increased their food intake after several weeks of starvation. (MARSIPAN)

For example, someone who has been almost nothing could decide to recover and start eating a regular amount of food straight away. Their serum phosphate level could then fall dangerously and require oral phosphate supplements to correct this abnormality.

Electrolyte disturbances (primarily decreased levels of phosphorus, magnesium, or potassium) occur immediately upon the rapid initiation of refeeding-commonly within 12 or 72 hours-and can continue for the next 2 to 7 days. Cardiac complications can develop within the first week, often within the first 24 to 48 hours, with neurologic signs and symptoms developing somewhat later. (from here)

Re-feeding syndrome is characterised by rapid reductions in certain electrolytes, such as phosphate and potassium, caused by rapid transport into cells, and the resulting cardiac effects can be fatal. Avoidance of the syndrome can be achieved by gradually increasing nutritional intake. There is substantial variation in opinion about the level at which to start re-feeding a patient with anorexia nervosa. Some units follow NICE (2006) guidelines for adult nutrition support, which recommend starting at 5kcal/ kg/day for a patient weighing 32kg. Although the guidance excludes eating disorders, it is considered by some to be relevant to patients with severe anorexia nervosa. However, there is wide variation in its application, some physicians and dieticians applying it strictly and others regarding it as not applicable to this patient group. One of the very few published guidelines in this area from the USA, referring to the treatment of children with anorexia nervosa (Sylvester & Forman, 2008, p. 393), advises:  Patients start on 1250–1750 calories, depending on the patient’s intake prior to hospitalization and severity of malnutrition, and advance by 250 calories daily. For patients with very low weight (<70% average body weight), the protocol is altered and caloric intake requirements may be decreased to avoid re-feeding syndrome, and advancement takes place over a longer period. (MARSIPAN)

Sometimes physicians are torn between the risk of re-feeding syndrome, and the risk of further weight loss due to not eating enough which then could mean death. In addition;

One physician in the group suggested that it was perhaps less harmful to risk re-feeding syndrome, which can be monitored and corrected, than brain damage and death caused by low glucose in a patient with hypoglycaemia. It was also commented that if higher calorie levels were thought to be essential (e.g. to correct low glucose), a critical care approach with constant monitoring and correction of abnormalities should be considered. (MARSIPAN)

When it comes to dangerously sick patients with anorexia nervosa, the risks have to be weighed up and a decision reached as to what is more dangerous for the patient who is in a life-threatening condition. On the subject of avoidance of re-feeding syndrome:

Avoidance of re-feeding syndrome can also be encouraged by restricting carbohydrate calories and increasing dietary phosphate. When patients are prescribed oral or enteral nutritional supplements, consideration should be given to the use of high-calorie supplements (e.g. 2kcal/ml) as they have lower levels of carbohydrate and may therefore be less likely to produce re-feeding syndrome. Moreover, the diet should be rich in phosphate (e.g. milk) to help avoid the syndrome. The total fluid intake can easily exceed safe levels, and the recommendation is 30–35ml/kg/24h of fluid from all sources. (MARSIPAN)

Remember that the MARSIPAN Guidelines described above are based in a hospital setting. 

As for more understanding on what refeeding syndrome is:

To understand what happens during refeeding syndrome, first review the pathophysiology of malnutrition. Normally, glucose is the body’s preferred fuel, coming from the intake of carbohydrates. As the malnourished body loses access to carbohydrates, it shifts to catabolism of fat and protein. With this shift, the body’s production of insulin drops in response to a reduced availability of glucose. This adaptive change to protein breakdown during prolonged malnutrition also leads to a gradual loss of cellular and muscle mass, often resulting in atrophy of vital organs and other internal structures, including the heart, lungs, liver, and intestines.
Serious complications may occur as respiratory and cardiac function declines due to muscular wasting and fluid and electrolyte imbalances. Metabolic rate, cardiac output, hemoglobin levels, and renal concentration capacity also decrease.
The body is now surviving by very slowly consuming itself…
When a malnourished patient is given aggressive nutritional support, such as PN, a number of events ensue. These are primarily driven by the change in insulin secretion as a result of the shift from protein metabolism to carbohydrate metabolism. The increase in glucose levels, which results from the composition of the nutritional support formula, increases insulin release by the pancreas. This in turn promotes cellular uptake of glucose along with electrolytes, primarily phosphorus, magnesium, and potassium. The result can be a life-threatening depletion of these vital electrolytes. (from here).

Also,

[RFS] is extremely rare but is more likely to occur in a young person with rapid weight loss and a BMI – from here.

As said above, refeeding syndrome is rare. People at risk are generally people are underweight, and have severely restricted for a week or more. However, if you have been eating less than 1000 calories for a week or more, are excessively exercising, or have been purging frequently, you may be at risk of re-feeding syndrome, regardless of BMI. If this is the case please see a doctor to determine the risk of RFS. Depending on your risk you may be hospitalised to be monitored there, you may be monitored by your doctor, or you may be okay to go home and just get your parents or flatmates to keep an eye on you.

You are most at risk in the first 24-72 hours, so don’t panic if you have upped your intake quickly and were not aware of RFS and have been eating a normal amount for a couple of weeks. You will be out of the danger zone by now.

Milky products are also really good for those with lowered phosphate levels, and are easier for the body to absorb.

As said above, there is also a problem with people being over-cautious and not increasing by enough or fast enough. If you are being monitored in a hospital setting, the staff there will decide what your calorie increase rate is. If you are home and have been deemed to be at very low risk, I advise increasing your calorie intake by 250 calories every 2-3 days until you reach 2000 calories. From there it is safe to jump to your 2500-3000+ calories.

As for a more in-depth look at warning signs and symptoms:

First, let’s look at some normal functions of phosphate. It’s needed to produce adenosine triphosphate (ATP), which provides energy for almost all cellular functions. Phosphate is an essential part of RNA and DNA, and it’s needed in red blood cells for 2,3-diphosphoglycerate production for easier release of oxygen to the tissues. Patients with signs and symptoms of hypophosphatemia or phosphate levels below 2 mg/dL require oral or I.V. phosphate replacement.

Refeeding-induced severe hypophosphatemia (serum concentration less than 1 mg/dL) can result in respiratory failure from a decrease in available ATP, which is needed to maintain the diaphragm’s normal contractility. In addition, hypophosphatemia can cause red and white blood cell dysfunction, muscle weakness, and seizures. Other factors that can contribute to hypophosphatemia include vitamin D deficiency and excessive intake of antacids, which block phosphate absorption.

Hypokalemia (serum levels below 3.5 mEq/L) and hypomagnesemia (serum levels below 1.8 mg/dL) are also frequently associated with refeeding syndrome. Mild decreases of potassium and magnesium may cause nausea, vomiting, constipation, diarrhea, muscle twitching, or weakness. A more severe depletion of the serum concentrations of potassium and magnesium can cause dysrhythmias, cardiac dysfunction, skeletal muscle weakness, seizures, and metabolic acidosis.

Your patient with refeeding syndrome may develop muscle weakness, tremors, paresthesias, and seizures… In addition, she may have cognitive changes, including irritability and confusion. (from here)

Please take note of this post. Although rather dry, it is very important.