Refeeding syndrome is a serious medical and potentially fatal condition that usually occurs when a malnourished person (for example, an individual with an eating disorder or history of prolonged fasting) reintroduces food too quickly after a long period of food restriction. 

Read on to find out more about refeeding syndrome, including how it develops, its main symptoms and complications, who is most at risk, and to learn when to seek medical attention.

Introduction 

Refeeding syndrome is a serious medical and potentially fatal condition. It occurs when a malnourished person who has been starved of food for a long time starts eating more food again, especially if they reintroduce food at a fast rate.¹

The exact prevalence and incidence of refeeding syndrome is unknown.² However, refeeding syndrome seems to be more common in people who:¹

• Have or have had eating disorders such as anorexia nervosa or bulimia nervosa 
• Have previously lost more than 10% of their body weight 
• Engage in prolonged fasting (where food is restricted for more than 7 days) 
• Have malabsorption disorders (such as chronic pancreatitis and inflammatory bowel disease) 
• Have long-term parenteral nutrition 
• Have cancer and chemotherapy 
• Have uncontrolled diabetes 
• Have chronic alcohol use 
• Abuse antacids or diuretics 

Causes of refeeding syndrome

When the body is malnourished and in a starved state, it makes several adaptations to conserve energy and nutrients. It slows down the basal metabolic rate (BMR) (the calories burned for survival) by as much as 20-25%. The body also starts to metabolise its own fat and muscle instead of carbohydrates.^1,2 

The body usually utilises two groups of biomolecules to metabolise carbohydrates: electrolytes (such as phosphorus, potassium, and magnesium) and vitamins such as thiamine (vitamin B1). Vitamin B1 acts as a cofactor. Therefore, it is essential for the activity of enzymes involved in carbohydrate metabolism to turn glucose (sugar) into energy). Starvation depletes electrolyte stores. That makes this process challenging and even dangerous to accomplish.

Once refeeding occurs, the sudden increase in carbohydrate (specifically glucose) levels causes insulin levels to rise. Insulin promotes the uptake of glucose into cells using electrolytes such as phosphate and magnesium. Phosphate, magnesium, and water are also transported into cells. This intracellular shift of electrolytes decreases their levels in the serum (blood). This is dangerous since the electrolyte levels are already extremely low due to starvation. Consequently, electrolyte deficiencies occur, which will be explained shortly below.² 

Signs and symptoms of refeeding syndrome

There are 6 main signs of refeeding syndrome, which can all cause severe complications. These include:¹

1. Phosphate deficiency

Phosphate deficiency or phosphorus deficiency (hypophosphataemia) is the most common feature of refeeding syndrome. It may give rise to the following symptoms:

• Muscle weakness
• Heart weakness (cardiomyopathy)
• Breathing difficulties
• Swallowing difficulties 
• Double vision
• Seizures 
• Coma 

Phosphate deficiency can result in organ failure and lead to death if left untreated.

2. Magnesium deficiency 

The symptoms of magnesium deficiency (hypomagnesaemia) may include:

• Nausea
• Vomiting
• Anorexia
• Tremors
• Muscle spasms
• Seizures
• Coma
• Cardiac ischemia 
• Abnormal heart rhythms (arrhythmia)

3. Potassium deficiency

Mild potassium deficiency (hypokalaemia) often does not result in symptoms. However, cases of severe hypokalaemia may cause:

• Muscle weakness
• Muscle cramps
• Fatigue 
• Severe constipation
• Arrhythmia
• Respiratory failure

4. Thiamine (vitamin B1) deficiency 

Thiamine deficiency mainly occurs when refeeding with carbohydrates in particular. It may result in:

• Delirium
• Vision problems
• Balance and coordination problems (ataxia)
• Hypothermia
• Amnesia
• Creation of false memories (confabulation)

5. Body-fluid disturbances

Refeeding syndrome causes changes in the balance of water and electrolytes (including sodium) throughout the body. This leads to either dehydration or fluid overload (hypervolemia). This may result in:

• Low blood pressure (hypotension)
• Muscle spasms
• Fluid build-up in the lungs (pulmonary oedema)
• Kidney dysfunction 
• Congestive heart failure 
• Seizures 

6. Blood sugar problems 

Refeeding with glucose in particular can cause hyperglycaemia (high blood sugar). Hyperglycaemia can result in:

• Headaches
• Blurred vision
• Frequent urination 
• Fatigue 

Preventing refeeding syndrome

To prevent refeeding syndrome, people at risk of refeeding syndrome should work with a healthcare professional to:²

• Check and closely monitor electrolyte levels, especially the levels of potassium, magnesium, phosphate, and calcium, for the first 2 weeks to make sure the patient has no electrolyte deficiencies.
• Provide supplementation. Before refeeding occurs, NICE advises patients to be supplemented with the following:
  • 200-300 mg of thiamine (vitamin B1) daily 
  • 1-2 tablets of high-potency vitamin B 3 times a day (or a full dose of intravenous vitamin B) 
  • A multivitamin or trace element supplement daily

Supplementation with potassium, phosphate, calcium, and magnesium is also recommended. 

• Perform gradual and controlled refeeding. NICE recommends that patients who have eaten little to nothing for more than 5 days start feeding on no more than 50% of their energy requirements. Patients at high risk of refeeding syndrome should feed on a maximum of 0.042 MJ/kg/day (24 hours). Afterwards, these patients should gradually increase the feeding over the next 4-7 days. 

The refeeding syndrome may also be prevented by:¹ 

• Avoiding drug, alcohol, or medication overuse
• Only engaging in prolonged fasting when medical supervision is provided 

Diagnosis 

A healthcare professional will diagnose a suspected patient with refeeding syndrome. This is done by performing a series of tests in the following order:¹

1. Physical examination and medical history: During the process of refeeding, a healthcare professional will check the patient's vital signs. These include body temperature, blood pressure, heart rate (pulse), and breathing (respiratory) rate
2. Laboratory tests: If the patient is found to have abnormalities in any of the vital signs described above, the healthcare professional may order a blood test to be performed. A blood sample is taken and then sent to a laboratory for testing. The blood test helps identify any imbalances the patient may have and in which electrolytes in particular. This aids in the management and treatment of the illness 

It is important to mention that electrolyte deficiencies do not always appear on a blood test. They may only become evident after refeeding occurs. This is why it is imperative that electrolyte levels are monitored daily and patients’ signs and symptoms are constantly checked. This is especially important during the first 5 days of refeeding as this is when refeeding syndrome often occurs. 

Management and treatment of refeeding syndrome

If refeeding syndrome is detected, the healthcare team will treat the patient by:^1,2 

• Decreasing the amount of food given, specifically carbohydrates in formulas
• Rehydrating with fluids slowly and carefully to avoid fluid overload
• Correcting any missing nutrients and electrolytes via supplements and/or an IV 

Summary

Refeeding syndrome is a serious medical and potentially fatal condition. It usually occurs 5 days after people who are severely malnourished reintroduce food back into their diets at a fast rate. 

The body requires electrolytes such as potassium, magnesium, and phosphate to metabolise carbohydrates. Unfortunately, electrolyte supplies become very low during starvation. Refeeding (especially with carbohydrates) causes electrolytes such as potassium, magnesium, and phosphate to move from the blood into cells. This shift of electrolytes further depletes their levels in the blood. This leads to phosphate deficiency (hypophosphataemia), magnesium deficiency (hypomagnesaemia), and potassium deficiency (hypokalaemia). 

Hypophosphataemia is the hallmark feature of refeeding syndrome. Hypophosphatemia mainly results in cardiac (heart), respiratory (lung), and muscular symptoms. These symptoms can lead to organ failure and eventually death if left untreated. In addition to electrolytes, refeeding syndrome can also give rise to deficiencies in vitamins such as vitamin B1. Hyperglycaemia (high blood sugar), fluid overload, or dehydration are complications that might occur from electrolyte deficiencies in refeeding syndrome. 

Refeeding syndrome can be prevented by: 

• Reintroducing food and fluids slowly and gradually 
• Closely monitoring patients’ electrolyte levels daily. This is especially true during the first 5 days of refeeding as that is when refeeding syndrome usually occurs 
• Taking supplements to correct electrolyte and vitamin deficiencies 

It is crucial to seek immediate medical attention if you experience any of the signs and symptoms of refeeding syndrome. The same applies if you or somebody you know is at high risk of refeeding syndrome. Factors such as having an eating disorder (e.g. anorexia nervosa), a history of prolonged fasting, or severe malnutrition, increase that risk. 

Early medical intervention is critical for managing the severe complications of refeeding syndrome appropriately.