DISCLAIMER: This answer is only about "how to break fast" and prevent refeeding syndrome in otherwise healthy adults, not in those who suffer from chronic alcoholism, eating disorders, cancer or other conditions.
Refeeding syndrome can occur within few days of rapid feeding that follows prolonged starvation lasting for more than 5 days. Symptoms can include weakness, muscle cramps, tingling, seizures and, possibly, death.
Refeeding syndrome occurs due to glucose that quickly enters the cells and drags phosphate, potassium, magnesium and vitamin B1 with it, resulting in hypophosphatemia and, less commonly, hypokalemia, hypomagnesemia and vitamin B1 deficiency. Sodium and water retention resulting in edema can also occur.
Prevention of refeeding syndrome:
- Slow feeding in the first week:
- after 5-10 day fasting: 20 Kcal/kg body weight/day
- after >10 day fasting: 10 Kcal/kg body weight/day
- Taking multivitamin supplements, including vitamin B1, daily for at least 10 days
- Eating usual foods, but taking care to get enough phosphates (meat, canned fish with bones, cheese, eggs) and potassium (potatoes, bananas)
- Avoiding foods high in sugars and other quickly-absorbable carbohydrates (fruit juice, soda, sweets, white bread, pasta cookies or rice) to prevent quick blood glucose shifts
- Drinking only as much water as necessary to maintain normal skin turgor and excretion of clear or straw-yellow urine, and avoiding excessive salt intake to prevent water retention (swollen ankles)
- Refeeding syndrome: what it is, and how to prevent and treat it (PubMed, 2008)
- The Importance of the Refeeding Syndrome (Hopkins Medicine, 2001)
- Refeeding syndrome – awareness, prevention and management (PubMed, 2009)
- Refeeding Syndrome: Recognition Is the Key to Prevention and Management
(Journal of American Dietetic Association, 2008)