There are several theories that lead a person to develop anorexia, but each individual case is unique. Anorexia is a need for control. Usually anorexia strikes women, but men can also develop the disorder. It usually starts around the beginning of adolescence, when your period begins.
There are deeper causes of anorexia and there are triggers that actually start the dieting itself. Deeper causes would be family dynamics, and triggers would be name calling and insinuations about looking better. Some of the deeply rooted reasons for anorexia come from perfectionism and overprotective mothering. At adolescence a girl might feel conflicted about taking on more independence and at the same time, feeling angry and rebellious towards her parents.
Usually, there is a trigger that starts the dieting. For instance, male figures in a girl's life may make comments about how she is plump, or she may overhear petty criticism of other girls who say something like "she should stop putting food in her mouth."
Some girls already have vulnerabilities about not being attractive enough. Any comments made about their looks, although there may be no intent to offend, are perceived negatively. There is a simultaneous desire to please and be independent of those comments.
The fact that a girl already feels insecure may make her vulnerable to an eating disorder. Anorexics are usually above average intelligence and read deeply into people's behavior. They may be the type that sees the backhanded insult embedded in the compliment. They generally see all the suggestions of others as insincere or emptily motivated. They are honest with themselves about what they see. If you want to reach out to one, don't minimize their perceptions as being exaggerated or overly negative.
Anorexics and bulimics may live double lives where they do as they please and sneer at authority figures whom they despise for their own top secret reasons. Knowing two girls with eating disorders, one who went missing and one who died for reasons that are still not known, I find it interesting that these two girls actually had some things in common.
First of all, they had unique personalities. They did their own thing even though they seemed bent on pleasing everyone else with their looks. Perhaps they could have been called recalcitrant. Their disorder seemed to say, "You said you liked me thin, you said you liked me thin, you said you liked me thin."
Secondly, they were withdrawn. They seemed uninterested in being with others. One used to just go off on her own, but if she had to be part of a group, she would only be superficially cooperative.
Third they were overachievers or they lived in their minds. They had an independent mental life as a secret world apart from the real world. They turned it on and off like a switch.
Anorexia and bulimia make one susceptible to other self-destructive behaviors. I once read that there is a link between bulimia and theft. Anorexics will abuse drugs to gain approval from others, but being so thin, they will sometimes die of cardiac arrest. All in all anorexics have low self-esteem and feel unloved.
Anorexia is a disease that seems hard to treat because anorexics can be secretive. They see people who want to make them eat as uninformed. They want help, but are too caught in their own obsessions. Their mind is too entangled in their own obscure opinions to go with you the full length.
Ironically, some anorexics work in eating disorder clinics. They treat other women and study the disease and its causes. Yet, their passion about the disease does not mean they are over the eating disorder.