Eating Disorders

Eating Disorders
Eating Disorders: are one category of mental disorder. Individualswith eating disorders have some problem with food, for example theymay overeat (e.g. obesity), undereat (e.g. anorexia), or vomitrepeatedly (e.g. ruminative disorder). There is some evidence thateating disorders are have a genetic basis but are also triggered byenvironmental stressors.Anorexia nervosaIt is literally a ?nervous lack of appetite?.
The main characteristics are as follows:
Deliberate and prolonged restriction of calorie intake and
considerable weight loss.
Intense fear of gaining weight, but anorexics are often very
hungry and preoccupied with food.
Anorexics have a disturbed body image ? they usually continue to
see themselves as overweight despite a large weight loss.
Amenorrhoea (no menstrual cycle).
Largely a problem with middle class, adolescent girls.
It is sometimes seen as a modern problem.
There are two types of anorexia: The restricting type ? constant
fasting, and the binge eating/purge type ? those who periodically
binge and purge.
Bulimia nervosa It is a more common problem than anorexia and probably more related to dieting. The main characteristics are as follows:
Periods of compulsive bingeing followed by forced vomiting or the
use of laxatives or other means.
Binge-eating is reasonably common among dieters. When it occurs
more than 2 times a week and for over 3 months, it is considered
abnormal.
Bulimics are obsessive about their weight, though it is usually
nearer normal than anorexics. Most of them are within 10% of
correct body weight.
Explanations of Anorexia nervosa: The biological (medical) explanations Genetic Transmission: Twin studies illustrate this. Holland et al found a 55% concordance rate for identical (MZ) twins. (Monozygotic). Compare with only 7% for non-identical (DZ). Evaluation: The fact that not all MZ twins develop the disorder means that genetic transmission cannot be the sole explanation. Biochemical abnormalities: Disordered hormones may be a cause. Amenorrhoea may occur before weight loss, which suggests a disorder of the endocrine system. Fava et al found changes in the levels of serotonin and also nor adrenaline in anorexics. Evaluation: Damage to the hypothalamus may result in loss of appetite, as well as disturbances to menstruation. Evaluation of biological explanations Strengths:
Biological models can explain why anorexia is related to
adolescence ? for the reason that it is a time of hormonal change.
The diathesis-stress model proposes that genetic vulnerability
must be part of the explanation, though there also needs to be
some trigger (stress).
Weaknesses:
Biological explanations can?t explain the recent increase in cases
of anorexia.
It isn?t always possible to distinguish cause and effect.
Key Study for biological explanation of Anorexia Nervosa: Holland et al. (1988) Evidence for a genetic basis Aims: This study aimed to find out whether anorexia nervosa is related to genetic factors. One way to investigate this is to look at twins who develop this disorder. If anorexia is genetic then we would expect more MZ twins pairs to develop anorexia than DZ twin pairs because they have identical genes. (Whereas DZ twins share 50% of their genes). Both kinds of twins are assumed to share the same environment during development. Procedures: Twin studies are natural experiments. The participants in this study were 34 pairs of twins (males and females) and one set of triplets. Participants were selected because they were a twin and one member of the pair (i.e. triplet) had been diagnosed with Anorexia nervosa at a London hospital. Genetic relatedness (i.e. whether they were MZ or DZ) was established by blood group analysis or by use of a physical resemblance questionnaire. Both twins were interviewed to establish presence or absence of an eating disorder, and this data was used to confirm or diagnose anorexia. Findings: Far more MZ twins (56%) were concordant for anorexia nervosa than DZ pairs (7%). Concordant means that both members of the pair had the disorder. In three cases the partner twin was found to have other psychiatric illnesses, and two others had minor eating disorders. Conclusions: These findings suggest that anorexia has a strong genetic basis because it occurred more when individuals shared the same genes than when they were simply related. However, concordance was not 100% which suggests that genes simply predispose individuals to develop an eating disorder (or other disorder). Only in certain circumstances (environmental triggers) does anorexia develop. Criticisms:
Since the twins were reared together they also shared
environmental influences and this may be greater for MZ twins who
look and behave more similarly than DZ twins, and therefore are
treated more the same.
It could be that one twin imitates the twin who developed the
disorder first. However, some of the twins developed the disorder
when living in separate countries. This would also not explain the
difference between MZ and DZ twins.

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