Prolonged starvation can lead to decreased mineral levels (for example, phosphorous, potassium, and magnesium). These may be masked during starvation because adjustments in kidney function and reduced metabolic needs mean normal blood electrolyte levels are maintained. (In other words, lab results may not reveal existing mineral deficiencies). Starvation also causes muscle wasting, including cardiac muscle.
When the starved body receives an influx of nutrition, insulin levels increase rapidly. Insulin causes the cells to uptake potassium, phosphorous, and magnesium, further reducing electrolyte levels in the blood. In addition, the cells need more of these minerals to provide for increased metabolic activity (for ex. Phosphorous is needed for ATP). Finally, carbohydrate infusion can cause water and sodium retention.
Electrolyte imbalance/deficiency can result in heart arrhythmia or even failure (the risk is worse for those with the weakest hearts), mental confusion, muscle weakness, and respiratory problems/failure along with a host of other problems.
RS can be treated or prevented if electrolyte levels are monitored and replaced as needed when the feeding is initiated, if adequate protein/fat is included in the nutritional regime, and if sodium intake is limited. Also, calorie levels should be gradually increased over a period of days.
The take-home message seems that the biggest danger for people with EDs such as anorexia may occur during early stages of increased food consumption after a long period of restriction, the need for key minerals greatly increases with sudden increases in nutritional intake, and that misinformed efforts at self-recovery (without medical monitoring) might be quite dangerous(!)
Let me know if you can't access the pdf file (the text is quite long, so I didn't include it here).