Extensively studied, bulimia nervosa is a condition where individuals have persistent concerns with their body image and weight. They have frequent episodes of binge eating followed by either purging or fasting for days to compensate for the large amount of food eaten earlier. A large amount of research has been dedicated to finding the possible influences that drive bulimics to such extreme eating behaviors. Findings are not exclusively supporting either the nature or the nurture side of the debate. Rather, they add insight to the whole picture of the disorder. This essay will discuss some findings that provide a nature view of bulimia and some that provide a nurture view.
From The Nature Perspective
Bulimia nervosa is now known to run in families. Studies on correlations between those with bulimia nervosa and their first-degree relatives have generally found high lifetime occurrence rates. A study by Strober and his colleagues (2000), conducted with first degree relatives of bulimic individuals, have found that the lifetime rate of having full bulimia is much higher among those who are closely related to bulimic patients than those of the never-ill comparison group. After interviewing and assessing both the relatives and the ill probands, the researchers found that the lifetime prevalence rate of first-degree relatives of bulimics were 4.4 times higher than the prevalence rate of relatives for those of the never-ill comparison group. In other reports, the prevalence rate for relatives of patients with eating disorders was as high as 10 times greater the prevalence rate for relatives of unaffected patients (Bulik, 2005; Hudson et al., 1987; Lilenfeld, 1998; Kassett et al., 1989).
Further research in twin studies has supported the hypothesis that genetics have a big contribution for bulimia nervosa. In a 1991 study, Kendler and his colleagues interviewed 2163 twins and found concordance rates of 22.9% for monozygotic twins and 8.7% for dizygotic twins. Their findings provided support for a moderate role of gene influence for bulimic individuals. Wade et al. (2000) had similar findings. In their longitudinal experiment, they interviewed 854 pairs of twins, of which 497 were monozygotic, 354 were dizygotic, and 3 were of unknown zygosity. They found that the group membership of a monozygotic twin (never binged or binged and had bulimia) could determine the membership of the other twin. The odds ratio of this happening was 4.17 compared to 1.36 for dizygotic twins. The two aforementioned studies found evidence that genetic factors exist for binge eating and bulimia among female twins. However, it is important to note here that the participant pool for both studies were Caucasian females from the Twin Studies Registry of Virginia state in the United States. So although the studies were conducted nearly a decade apart, the fact that they use the same pool of participants may have influenced the statistical results for both experiments.
Studies for genetic contributions are not complete without looking at the environment of which the individuals of interest were raised in. Twin studies offer important insight into genetic influences of eating disorders but do not completely rule out the influences of the environment. Klump and her colleagues (2009) were the first to look into this issue with their adoption study. They pulled biological and adoptive female sibling pairs from the Minnesota Center for Twin and Family Research. Disordered eating habits were assessed with the Minnesota Eating Behaviors Survey (MEBS). Further they used a univariate sibling model, termed ACE, to estimate relative contribution of genetic, shared environment, and nonshared environment influences to factor in to the total MEBS score. Klump and colleagues found that the scores between adoptive and biological sibling pairs were statistically significant (r’s = .29-.46), whereas the scores for adoptive sibling pairs were not. This suggests that there are significant genetic influences for bulimia nervosa symptoms.
Almost all family, twin, and adoption studies provide evidence in support of genetic influences in disordered eating behaviors that lead to bulimia nervosa. It is important to note that although there are similar findings from many family and twins studies, there is still great variability between the results. Studies were mostly based on self-reports or one-on-one interviews, and there are no standard measures by which to analyze these results. As such, different coding methods for interview responses may produce inconsistencies in statistical reporting. There is also a categorical problem. As full-blown bulimia is rare and often unreported, many studies make do with by looking for disordered eating that are symptoms of bulimia. This results in inconsistent operationalization of terms. Also, twin studies make the assumption that twins are raised in the same environment and are treated equally by their parents. Such assumptions may result in erroneous interpretations that results are all of genetic influences.
From The Nurture Perspective
Just as much as there are empirical findings in the biological dimension of eating disorders, there is just as much, if not more, for the psychological, social and socio-cultural dimensions. Influences can be divided into two main factors: interactions with one’s own body and interactions with others. The latter factor can be further divided into internal influences (e.g., familial backgrounds, parental attitudes, peer pressures) and external influences (e.g., standards of beauty set by mass media, cultural values and norms). This part of the essay will focus on the later factor.
The family histories of bulimic individuals have a significant role in influencing their eating behaviors. Studies have shown that parenting styles are very important in driving the eating behaviors of adolescents. Enten and Golan (2009) found significant, negative correlations between young girls’ body dissatisfaction and the drive for thinness with their perception of their father as authoritative. Furthermore, Haycraft and Blissett (2010) found that high levels of eating disorder symptoms were associated with authoritarian and permissive parenting styles. Controlling parents may attempt to force adolescents to be more conscious of their weight by pushing them to gain weight or to lose weight by developing certain eating patterns. It has also been found that the quality of family and peer relationships does not strongly predict body dissatisfaction but rather the teasing and criticism about body shape and weight do. Mothers and peers who diet to lose weight send indirect messages to adolescent girls that encourage dieting and reinforce the importance of being thin (Vincent & McCabe, 2000). They inadvertently become the role models for these body-conscious girls.
Not surprisingly, a large amount of research has looked into the role of the media in eating disorders. The media sets unrealistic and hardly attainable standards of beauty that drives young men and women to be conscious of their body shape and weight. The social environment serves as a chronic reminder of the importance of beauty, and girls soon begin to evaluate themselves based on these external standards (Pelletier & Dion, 2007; Stice, Shaw, & Nemeroff, 1998). Some researchers explain this the route to eating disorder as a process of social comparison (Harrison, 2001). This self-evaluating behavior involves multiple processes that reinforce each other. It is possible that an adolescent is vulnerable to criticisms and evaluations from family and peers. Outside of their social interactions, these adolescents see models in billboards, magazines, and television shows advocating slim bodies. They feel greater degrees of body dissatisfaction and begin to diet. They may then receive positive reinforcement from parents and friends who notice they are thinner than before. The reinforcement further pushes them to diet, possibly in unhealthy ways.
Thoughts on Nature and Nurture
Bulimia nervosa is an interesting disorder of many causes. The vast amount of research conducted in this area of eating disorders show that bulimia is not caused by any single factor but rather the interaction of many factors. Genetic contributions, family background, parental attitudes, peer pressure, media exposure – all these factors have been at the center of focus in studies and no one study can resolutely conclude that one factor drives them all. I believe the best way to look at this nature and nurture dilemma is view it from a diathesis-stress model approach. Genetic studies provide strong support that genets may predispose individuals to be more prone to developing an eating disorder. At the same time, studies on family and media influences also demonstrate that these elements should not be ignored. An individual’s genes may genetically predispose her to produce too much dopamine. (High dopamine levels are related to a decrease in appetite.) Furthermore, family urgings to lose weight or to be more conscious of what foods are consumed may act as stressors for the individual to limit eating all together. Thus, it is better to view bulimia nervosa as an eating disorder of many causes rather than just a result of nature’s construction or nurture’s negligence.
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