What is refeeding syndrome?
Refeeding syndrome is a potentially life-threatening metabolic complication that can occur when carbohydrates are reintroduced too rapidly after a prolonged fast (typically over 72 hours) or period of starvation. When insulin spikes in response to carbohydrate intake, it drives phosphate, potassium, and magnesium into cells, causing dangerous drops in serum electrolyte levels. This can lead to cardiac arrhythmias, respiratory failure, and muscle weakness.
For fasts under 18–24 hours, refeeding syndrome is not a realistic concern. The risk increases with fast length. For any fast over 72 hours, a slow, stepped reintroduction of calories — prioritising liquids and then small amounts of easily digestible food before returning to full meals — is strongly recommended.