http://web4health.info/en/answers/ed-psy-abuse.htm
A research-worker connected an electrode to the reward center in the brain of a mouse. Every time the mouse pressed a small level the reward center was stimulated, with the result that the mouse no longer wanted to eat or play with the others, but was content with continual stimulation until it died.

The reward center in the brain has evolved through natural selection and aids behaviour which may be of value for survival and reproduction. However, drugs stimulate the reward center without aiding survival. Compulsive eating and overweight aid survival because natural selection has helped these people to store nourishment which can be used if times get hard. Gambling addicts make use of the reward center without eating food or taking drugs.

The reward center can also be stimulated by injury. This is a protection against being made completely inactive by pain. This has led to a type of abuse where people have deliberately cut themselves in order to get a kick or as help against unpleasant feelings.

The same also applies to starvation. The initial feeling of hunger goes over after a few days if the calorie intake is less than 400 a day. The unpleasantness is followed by serene calm. Starvation reduces psychic discomfort.

Natural selection has aided those who can function despite starvation. Both overeating and starvation stimulate the reward system and increase the ability to survive during times when we involuntarily change from good to poor access to food.

Anorectics choose starvation because the alternative is binge eating or psychic uneasiness and anxiety. The feeling of self-control is used to suppress awareness of unpleasant feelings in the same way as drug addicts use drugs to suppress feelings.

Before anorectics become extremely emaciated they may be admired for their appearance. Our unnatural ideals of beauty are responsible for this, and the risk of starvation abuse is increased.

Those who work with the clinical treatment of eating disorders know that at different periods of life the same person may shift between anorexia, bulimia and binge eating. My research and those of others, shows that there are similarities of personality in this area: anxiety, depression, stress sensitiveness, poor contact with feelings and physical perceptions. The probability that the illness will reveal itself as anorexia is greater in those who also have strong self-control and poor self-esteem.