"[by] my junior year of high school, that's when I really started bingeing and purging. Food was my crutch; it was how I dealt with emotions and uncomfortable situations." - Katharine McPhee, American Idol runner-up (2006)
Scientists have been working on this very same question for over a quarter of a century. And the answer is not simple.
Bulimia nervosa (BN) is an eating disorder where a person eats a large amount of food in a short period of time, then uses some type of behavior to avoid weight gain... vomiting, misusing laxatives, over-exercising, etc.
The bingeing is a reaction to some sort of stress (e.g. "Eating makes me feel better"). The vomiting and other behaviors that follow are due to a sense of guilt or disgust (e.g. "Eating will make me fat").
The most susceptible age for developing bulimia is mid- to late adolescence (16-18). BN has also been found in teens under the age of 14, but this is quite rare.
Did you know? BN affects about 1% of the population and roughly 80% of bulimic patients are female. It is more common that anorexia nervosa. As for why some people develop BN, there are many possible reasons. These include psychological, environmental and genetic factors.
Psychological and Environmental Factors
Those with BN have a low self-esteem and tend to be impulsive with little tolerance of boredom. They are often extroverted and considered perfectionists who have a fear of failing or not fitting in with those around them.
Bulimics also have a difficult time in coping with stressful events. Examples that could trigger the illness are: moving to a new school; the death of a close friend or relative; the divorce of parents; breaking up with a boyfriend; sexual or physical abuse.
How someone gets along with their parents can also make them more susceptible to BN. For example, the risk of BN is higher if parents are indifferent to their feelings or there is a lot of family conflict going on.
Now you may be reading this and saying "I've had a lot of stress at school and my parents can really get on my case sometimes. But I've never had the urge to binge and purge. What's up with that?"
Well, as it turns out, there's good evidence that our genes determine how vulnerable we are to BN and other eating disorders. Although there is still much to learn, let's have a brief look at what is known so far.
- Role of Genetics
- BN is hereditary
- One way scientists have determined that BN involves genetic factors is by looking at the medical history of families.
Did you know? Studies have shown that there is a 4-times greater risk of developing BN if a family member or relative has this eating disorder.Another more reliable way is by studying twins. Identical (monozygotic) twins share 100% of their genes, whereas fraternal (dizygotic) twins share 50% of them. Since BN is more common in identical twins, this is further proof that genes play a significant role in this disorder.
Did you know? About 50 to 80 percent of the variance in the risk of developing BN is due to genetic effects. Candidate genes
Having identified that BN has a genetic basis, researchers are now trying to identify what genes (units of DNA) may be involved. This is not an easy task...
Did you know? Each cell in our body has between 26,000 and 38,000 different genes.
While the research is still in its early stages, scientists have learned a few things. For instance, many studies have shown that a "bulimia gene" does not exist. Instead, there seems to be a number of genes involved, each contributing a relatively small effect.
Did you know? The DNA that carries our genes is packaged in 23 paired chromosomes; one we inherit from our mother, the other from our father.
BN has been associated with genes on chromosomes 10, 14, 16. Also, there is evidence to suggest that someone with genes (or mutations) involved in BN will not necessarily develop the eating disorder. Other factors, such as stress and family relationships, are needed to "trigger" bulimic behaviors.
Bulimia nervosa is a very complex illness and this makes treatment a challenge for physicians. The most effective is cognitive behavioral therapy (CBT), which has the patient self-focus on identifying environmental triggers, thoughts and feelings that lead them to binge and purge. Scientists studying the genetics of BN are hoping their research will help lead to alternative forms of treatment.
Consult the National Eating Disorder Information Centre, a Canadian organization with many excellent articles and links on eating disorders.
Bulik, C.M. 2005. Exploring the gene—environment nexus in eating disorders. J Psychiatry Neurosci. 30(5): 335-339.
Murphy, B., and Y. Manning. 2003. An introduction to anorexia nervosa and bulimia nervosa. Nursing Standard. 18, 14-16, 45-52.
Pinheiro, A.P. et al. 2006. Genetics in eating disorders: extending the boundaries of research. Rev Bras Psiquiatr.
Schneider, M. 2003. Bulimia nervosa and binge-eating disorder in adolescents. Adolesc Med. 14(1):119-131
Photo credit: Cara Jean
CRAM Science would like to thank Dr. Stan Megraw for his help and expertise in answering this question. Stan is a writer/researcher specializing in science, technology and medicine. He has more than 30 years experience as contributing author for research institutes, universities, government agencies and non-profit organizations.