They do it because their brains are wired to. Girls with anorexia nervosa starve due to neural processing problems -- much like those associated with Asperger's disorder, a mild form of autism.
That's the latest theory of eating disorders, proffered in The Times (U.K.) by Janet Treasure, head of the Eating Disorders Unit at the South London and Maudsley Hospital NHS Trust.
In essence, faulty circuitry in the brain causes the restrictive, repetitive and obsessive behaviors of both disorders. Those with anorexia target the abnormal patterning toward food. Those with Asperger's focus intensely on other areas of interest.
Treasure's controversial thesis is based, in part, on commonalities that the two disorders share.
According to eating disorder experts, individuals with anorexia generally express trademark personality styles through food:
• Perfectionism. I want to look exactly like the fashion model ideal.
• Anxiety. I am terrified of being fat.
• Extreme rule-making. I will not eat more than 850 calories per day.
• Preoccupation with and rigid adherence to those rules -- to the point of social isolation. I plan all my meals two days in advance and count out my calories religiously so as to never go over my quota. I cannot eat out with others.
Experts say that individuals with Asperger's, too, have signature personality traits:
• Perfectionism (about areas of interest). I know my teacher is wrong about Route 41 crossing Highway 91 at Main Street, because I memorized the street map of my town.
• Hypersensitivity. The world outside my mind overwhelms me.
• Repetitive behaviors and rituals. I go to the library every day to read about cartography.
• Preoccupation and social isolation. My love of maps seem at odds with the rest of the world. I live in a parallel universe.
But while compelling, the observable similarities do not constitute scientific proof. " Just because it looks like a duck doesn't make anorexia an Asperger's duck, " says clinical psychologist Richard Pomerance, Ph.D, who has seen a number of Asperger's patients in his private practice near Boston. He points out that there are at least as many symptoms of Asperger's -- difficulty interpreting facial expressions and other social cues, for example--that do not show up in most anorexics.
Controversy aside, Treasure's theory certainly casts eating disorders in a new light. She says that anorexia is a disease grounded in human genetics and neurobiology. Genes orchestrate behaviors by coding for neurochemicals that signal each other in the brain, sometimes in abnormal ways.
This line of thinking is catching on within the eating disorders community. Researchers are using tools like DNA sequencers and PET scanners to "look under the hood" at the brainwork behind self-starvation behaviors.
Molecular biologists are hunting down the genes for anorexia that might seed the mind with a predisposition for anorexia.
The strongest candidates include genes involved with the serotonin system (which controls mood); dopamine centers (related to food repulsion, hyperactivity, and obsessive compulsive behaviors); and opioid receptors, (involved in reward and feeding control).
Other researchers are scanning the brains of individuals with anorexia for clues to the processing centers that might go awry. Again, serotonin pathways top the list.
Even evolutionary biologists are stepping up to the plate and offering their own hypotheses as to why anorexia lingers in the human species. At first blush, anorexics should be out of the game, given that infertility is a common effect of the disease. The answer may be that those who can exist on minimal calories during times of scarcity can keep the tribe alive and, in doing so, pass the culprit genes on to the next generation. It's survival of the species rather than the individual that matters.
But these biological underpinnings are only part of anorexia's complex mechanics, and Treasure is careful not to dismiss studies that point to culture and psychological issues as causes of and catalysts for eating disorders. Those studies do abound. For example, there is Anne Becker's work showing that the introduction of television into a population of Fijian teenage girls caused a surge of eating disorders in just three years.
Numerous studies show that sexual abuse, trauma, and even bullying can catalyze eating disorders.
So it seems that anorexia nervosa is rooted in both nature and nurture. From the nature and nurture perspective, a person may be born with "bad" genes, which produce faulty neurotransmitters and/or circuits. An individual with such a genetic make-up is a time bomb for distorted thinking about body image. Then, something in the person's environment eventually may light the fuse.
This makes sense when I hear stories like those of Laura, 65, whom I interviewed for Lying in Weight: the Hidden Epidemic of Eating Disorders in Adult Women. She was diagnosed with anorexia as a teen, recovered by 20, relapsed at 48, then recovered again. Laura is an identical twin. Her sister never had anorexia, and is, in fact, obese.
How do we explain the phenomenon of Laura and her sister, where two women share exactly the same genes but only one gets anorexia? Same genetic makeup, different life experiences.
As psychologist Cynthia Bulik, Ph.D. at the University of North Carolina, Chapel Hill, sums it up, "Genes load the gun. Environment pulls the trigger."
Follow Trisha Gura on Twitter: www.twitter.com/SciWriterPhD