Refeeding Syndrome

How refeeding syndrome happens

During starvation, the body switches from burning carbohydrate to burning fat and protein. Insulin falls. Stores of phosphate, potassium and magnesium inside cells become depleted, even though blood levels may look normal because they are maintained at the cells' expense. Thiamine (vitamin B1) stores also run low.

When carbohydrate is reintroduced:

1. Insulin surges, moving glucose into cells.
2. Phosphate, potassium and magnesium follow glucose into cells, and blood levels fall sharply. Phosphate is needed to make ATP, the cell's energy currency, so muscles, including the heart and breathing muscles, weaken.
3. Thiamine is used up in carbohydrate metabolism, which can trigger Wernicke encephalopathy.
4. Sodium and water are retained, causing swelling and fluid overload in a heart that has shrunk during starvation.

Who is at risk

The NICE criteria are widely used to identify adults at high risk.

One or more of:

• BMI under 16 kg/m²
• unintentional weight loss of more than 15% in the past 3 to 6 months
• little or no nutritional intake for more than 10 days
• low potassium, phosphate or magnesium before feeding

Or two or more of:

• BMI under 18.5 kg/m²
• unintentional weight loss of more than 10% in the past 3 to 6 months
• little or no intake for more than 5 days
• a history of alcohol misuse, or drugs such as insulin, chemotherapy, antacids or diuretics

Common situations

• Anorexia nervosa and other restrictive eating disorders
• Chronic alcohol use disorder
• Cancer, especially of the head, neck and digestive tract, and patients receiving chemotherapy
• Older adults with weight loss, dementia or after a long hospital stay
• After bariatric surgery, prolonged vomiting or bowel obstruction
• Hunger strikes, famine or prolonged fasting
• Critical illness with several days without feeding
• Uncontrolled diabetes with weight loss

Symptoms and signs

Many people have abnormal blood tests without symptoms. When symptoms occur, they reflect the low minerals and fluid overload:

High blood sugar can also occur early in refeeding.

How it is diagnosed

There is no single test. The ASPEN consensus defines refeeding syndrome as a fall in phosphate, potassium and/or magnesium by 10% to 20% or more (mild) up to more than 30% (severe), or organ dysfunction from these drops or thiamine deficiency, within 5 days of starting or substantially increasing nutrition.

Monitoring usually includes:

• phosphate, potassium, magnesium, sodium, glucose and kidney function before feeding, then daily for the first few days
• ECG in high-risk patients, particularly with low potassium or magnesium
• daily weight and fluid balance, pulse, blood pressure and swelling checks

Prevention and treatment

Before feeding starts

• Identify risk using the criteria above.
• Give thiamine before or with the first feed, along with a B-vitamin complex, and continue for at least 5 to 10 days.
• Check and correct low potassium, phosphate and magnesium, but do not delay feeding for days to do so.

Starting feeding

• NICE recommends starting high-risk adults at no more than 10 kcal per kg per day, and as low as 5 kcal/kg/day in extreme cases (BMI under 14 or no intake for more than 15 days), increasing gradually over 4 to 7 days.
• In adolescents and adults with anorexia nervosa treated in specialist units, more recent evidence supports starting higher with close monitoring, because underfeeding slows recovery. Specialist eating disorder teams follow protocols such as MEED.
• Feeding may be by mouth, tube or IV, depending on the situation.

Ongoing care

• Replace phosphate, potassium and magnesium by mouth or IV as levels require.
• Restrict sodium and fluid if swelling or heart strain appears.
• Slow or pause the increase in calories if levels drop significantly or symptoms develop, then resume gradually.
• Continue multivitamin and mineral supplements.

Outlook

When risk is recognized and refeeding is managed carefully, serious refeeding syndrome is uncommon and most people recover fully. Severe cases, particularly with very low phosphate, can cause heart failure, respiratory failure, and death. Most problems occur in the first week; risk falls once feeding reaches the target and mineral levels are stable.

Frequently asked questions

What is the main sign of refeeding syndrome?

The hallmark is a drop in blood phosphate (hypophosphatemia) within the first few days of feeding, often with low potassium and magnesium. Clinically, it can cause weakness, breathlessness, swelling, heart rhythm problems and confusion, though many people have only abnormal blood tests.

When does refeeding syndrome occur?

It usually develops within 2 to 5 days of starting or increasing feeding after a period of starvation or very low intake. That is why blood levels are checked daily during the first week, when the risk is highest.

Who is most at risk of refeeding syndrome?

People with anorexia nervosa, long-term alcohol misuse, cancer, very low body weight, major recent weight loss, or little or no food for more than 5 to 10 days. Older adults with poor intake and patients in intensive care are also at risk.

Why is thiamine given before refeeding?

Carbohydrate metabolism uses up thiamine (vitamin B1). In people with low stores, feeding can trigger Wernicke encephalopathy, causing confusion, unsteadiness and eye movement problems, and can lead to permanent memory damage. Giving thiamine before and during early refeeding prevents this.

Can refeeding syndrome happen at home?

Yes, it can, for example when someone with a severe eating disorder or after a long fast suddenly eats large amounts. People at high risk should restart eating under medical supervision with blood tests, rather than on their own.