Eating disorders I find fascinating, because not only are they something that goes against our very need for survival, they seem to be extremely prevalent in a country that also mirrors extreme obesity, yet the causes for the two are very extreme differences in which body size matters as a control factor. Anorexics and bulimics are often set in combination with depression or intense anxiety disorders. The need for a controlling aspect such as either food, exercise, or body size becomes a stability platform in which is extremely scary and dangerous. This runs through my family and is very close to myself as well so it is more interesting to see it through the psych component as well.
http://www.psychologytoday.com/conditions/anorexia-nervosa