What are Eating Disorders?
An eating disorder is marked by extremes. It is present when a person experiences severe disturbances in eating behaviour, such as extreme reduction of food intake or extreme overeating, or feelings of extreme distress or concern about body weight or shape.
A person with an eating disorder may have started out just eating smaller or larger amounts of food than usual, but at some point, the urge to eat less or more spirals out of control. Eating disorders are very complex, and despite scientific research to understand them, the biological, behavioural and social underpinnings of these illnesses remain elusive.

The two main types of eating disorders are anorexia nervosa and bulimia nervosa. Eating disorders frequently appear during adolescence or young adulthood, but some reports indicate that they can develop during childhood or later in adulthood. Women and girls are much more likely than males to develop an eating disorder. Over 90% of people diagnosed with eating disorders are adolescent or young women. Eating disorders are real, treatable medical illnesses with complex underlying psychological and biological causes. They frequently co-exist with other psychiatric disorders such as depression, substance abuse, or anxiety disorders.

Biological Perspective
The biological perspective is a way of looking at psychological topics by studying the physical basis for human behaviour. It involves such things as studying the immune system, nervous system and genetics. Also considered are physical factors that directly affect the nervous system, including heredity, metabolism, hormones, disease, drug ingestion, and diet.

The biological approach suggests that Eating disorders are due to a physical cause, suggesting it could be due to something genetic within the body or brain; such as hypothalamus dysfunction or an imbalance of neurotransmitters. Gonwood (1998) suggests that genes may dictate these abnormal levels of neurotransmitter's or abnormal development of the hypothalamus. Klump (2000) further developed on this theory suggesting that people with anorexia or bulimia and their parents have an obsessive-compulsive personality disorder that produces perfectionist behaviour. This can be seen in their obsessive interest in food.

The hypothalamus dysfunction theory would suggest that animals have a “set weight” which is correct for their body, if this weight should increase or decrease then the body should make adjustments to regulate food intake to their “set weight”.
Garfinkel and Gardner (1982) suggested that a disturbed hypothalamus may be the cause of eating disorders, they proposed that any disturbance could lead to either the lateral hypothalamus or ventromedial hypothalamus to be constantly activated.
Neurotransmitter's such as dopamine, cortisol, leptin and serotonin are also suggested to play a large role in eating disorders, with an imbalance of these found in those with eating disorders, suggesting that they are contributors to increased/decreased appetites. Fava (1989) found altered levels of serotonin and noradrenaline in anorexics.

Increased serotonin activity in the brain is associated with a suppressed appetite and also with increased anxiety, obsessive behaviour, phobias and even vomiting. It may be that restricting food intake alleviates these related symptoms because, if no food is consumed, (in particular a substance called tryptophan, found in certain foods) then serotonin levels drop, therefore they feel better. Galla (1995) suggested that serotonin also plays a part in bulimia but in an opposite way to anorexia, with a decreased level found in those with bulimia, resulting in an enhanced appetite.

However, assuming eating disorders have a genetic cause, how can we explain the huge increases in reported cases in the past forty years and the incidence in certain parts of the World only. This suggests cultural factors rather than genetics.
Another consideration is that of Fichter and Pirke (1995) who starved normal individuals, which caused changes in their neurotransmitter's and hormone levels, suggesting that starvation causes the changes rather then vice versa.

Psychodynamic Perspective
The psychodynamic approach views behaviours as influences of internal conflicts, motives and unconscious forces. The belief is that if behaviours are discontinued without addressing the underlying motives that are driving them, that relapse will occur. Symptoms are viewed as expressions of the patient's underlying needs and issues and are assumed to disappear with the completion of working through these issues. The psychodynamic model does not address nutritional issues, food-related symptoms or behavioural rituals of the eating disorder.

There are several explanations of Eating disorders based on the psychodynamic model. One proposed by Freud is that the disorder represents an unconscious effort by a girl to remain pre-pubescent. As a result of over dependence on the parents. Some girls might fear becoming sexually mature. Since Eating disorders are associated with menstrual periods stopping, psychodynamic theorists see this as enabling them to avoid growing up.

Another psychodynamic account proposes that the disorder may allow a girl to avoid the issue of her sexuality. The weight loss that occurs prevents breasts and hips from becoming rounded, and the body takes on a ‘boy-like’ appearance. Psychodynamic theorists propose that this might be a way of avoiding the issue of sexuality in general & the prospect of pregnancy in particular.

A third psychodynamic account see an eating disorder as an attempt by adolescents to separate themselves from their parents & establish their own identities. Bruch (1991) argues that the parents of anorexics tend to be domineering, and the disorder represents an attempt to gain a sense of autonomy and control as ‘such children experience themselves as not owning their own bodies’. One way of exerting individuality is to assume control over what is most concretely one’s self, the body. Thinness & starvation are signs of self-control & independence.

The main issue with these explanations is that they are difficult to prove wrong, Bruch (1991) developed her theory on the basis of examining many case studies of anorexia and producing an interpretation of the casual factors.

However, the main problem with these theories is that they do not explain the massive gender difference in the incidence of eating disorders, surely as many boys suffer from domineering parents as girls.

Behaviourist Perspective
The behavioural approach is based on the concept of explaining behaviour through observation, and the belief that our environment is what causes us to behave differently or suffer illnesses. Behaviour can be observed in terms of responses to certain stimuli. For example, a person being asked to hold a book (stimulus) would respond by holding the book. This Stimulus-Response Theory forms the basis of conditioning, which suggests learning in humans and animals can take place through the association of a response with particular stimuli. Behaviourism also assumes that we are born as a blank slate (tabula rasa) and so equal at birth. It is environmental factors rather than genetic or biological differences that make us behave differently. Behaviourism very much represents the nurture aspect of the nature-nurture debate.

From a behavioural perspective, eating disorders are considered a weight phobia. They involve the avoidance of fear-evoking stimuli, specifically food or unwanted body images.
Bulimic and anorexic individuals demonstrate compensatory behaviours, avoiding eating or purging in order to compensate for a perceived weight gain.

A second behavioural explanation suggests that slimming becomes a ‘habit, just like any other habit through stimulus response mechanisms (classical conditioning). The person first goes on a diet & after a while receives praise from others, for their attempts or their new slimmer appearance. Operant Conditioning then takes effect as the admiration from others further reinforces their dieting behaviour. Rewards may also come in the form of attention gained from parents by not eating.

Another concept that is supported by Becker (1999) is the influence of media (magazines, films etc) that create the social norm that 'thin is good'. We see that the thin models and film stars receive admiration and attention (vicarious reinforcement), and therefore we imitate the behaviour. This media explanation centres around indirect (vicarious) learning through operant conditioning (social learning theory).

However, these explanations do not explain why anorexics continue to diet even after they stop receiving compliments and are even told how awful they look and it does not explain individual differences, i.e. why some people develop the disorder and others with the same media pressures do not. All of us in the west are exposed to thin models but very few develop an eating disorder.

Conclusion
It is important to note, that there is no single explanation, all explanations fit together creating a long complex account, for example behavioural explanations on their own are not sufficient enough and may require the addition of one of the biological explanations to account for the development of the disorder in particular individuals. As is true with the biological explanation of inheritance, it's theory suggests that it is not the eating disorder it's self that is inherited but the vulnerability to developing the disorder, it suggests there must be a psychological stressor that triggers the disorder (the diathesis stress model). It would seem that not one approach can stand alone in a complete explanation of an eating disorder, therefore it would suggest the diathesis stress model is the best explanation.

Bibliography A. Natenshon, (1999), When your child has an eating disorder.
McLeod, S. A. (2007). Biological Psychology. http://glossary.feast-ed.org/types-of-eating-disorders-and-disordered-eating http://www.psychology.com/resources/eating_disorder.php http://www.psychologistworld.com/issues/behavioralapproach.php http://aqabpsychology.co.uk/2010/07/anorexia-and-bulimia-nervosa-explanations/