How are anemia and anorexia related?

They're not: But malnutrition and anemia are. If the anorexia is so severe that one becomes malnourished....Voila!

They aren't: I am impressed by how infrequently patients show signs of anemia and hypo-proteinemia (low protein) even when at a very low weight. It underscores the fact that lab values are not of much help when evaluating the medical status of a patient with anorexia nervosa, since the doctor may be falsely reassured. More important are vital signs, such as heart rate and blood pressure changes with standing.