The body's starvation process is complex.  Think of it as "survival mode."  Some of the most troubling issues are the gastrointestinal (GI) complaints, and these are often a patient's presenting complaint in a doctor's office.  Since GI issues can arise from a broad array of etiologies, the differential diagnosis can be difficult, and the underlying ED is often missed.  I've had GI issues, only to realize in hindsight that it was all a symptom of the ED.

The most common GI manifestations of starvation are constipation, early satiety, delayed gastric emptying and pancreatitis.  Nausea, bloating, and lactose intolerance are also common complaints.  Patients also tend to lose their hunger cues as a result of low leptin levels (a hormone that regulates appetite, which is secreted by adipose tissue).

Basically, what has happened is the GI tract has down-regulated it's functioning because it isn't being used.  When in starvation the body has to direct it's precious resources to keep you alive, and it's a waste of energy to keep a minimally used GI tract functional.  Hence, the slowed digestion, constipation, decreased digestive enzyme production, etc. 

How to resolve these issues?  Refeeding.  Food is the medicine.  Initially it's quite unpleasant, as we have to wake the GI tract back up.  The only way to resolve these issues is to force the body to adapt to normal eating again.  This is often quite distressing for the individual who is having to eat more than what the body is currently prepared to handle.  It can take several weeks, even months, for the GI issues to resolve.  But they do get better with time.  Normal eating leads to normal digestion.