New Brain Imaging Research Links Bulimia Nervosa To Measurable Brain Differences
Bulimia nervosa ranks second among eating disorders in both how common it is and how much burden it carries, yet remarkably little is known about what it looks like in the brain. Past imaging studies were small, and their findings kept contradicting each other.
New research pooled MRI scans from 13 sites worldwide to finally get a clear read, and they found consistent structural differences in regions tied to reward, sensory input, and social processing.
About the study
Researchers with the ENIGMA Eating Disorders Working Group pooled MRI scans collected at 13 sites around the world from 17 groups of participants. Altogether, they compared 369 females with bulimia nervosa to 417 females without an eating disorder, all analyzed through the same processing and quality checks so the numbers could be read side by side.
Participants were all female, which makes sense given the conditions is five times more prevalent in women. The subjects ranged in age from 12 to 53, with an average age of 23.6.
The researchers looked at three physical measures: how thick the brain's outer layer is, how much surface that outer layer covers, and the size of several structures buried deeper in the brain.
Reward and sensory regions measured smaller
The clearest differences between brains of women with bulimia nervosa and without eating disorders showed up in surface area rather than thickness.
Women with bulimia nervosa had less surface area in the the superior temporal and transverse temporal regions, the part of the brain's outer layer that handles hearing, reading social cues, and other incoming sensory information. They also had lower volume in the nucleus accumbens, a small structure deep in the brain that helps drive reward and motivation. Thickness of the outer layer showed no meaningful difference between groups.
These findings mostly held steady even after the researchers accounted for differences between cohorts in body weight, how long someone had been ill, depressive symptoms, medication use, and purging.
Binge eating tracked with the brain, purging didn't
The more interesting split came when researchers looked at symptoms rather than diagnosis. More frequent binge eating was linked to less surface area across a wider set of regions: the insula, which helps you sense signals coming from inside your own body; orbital and frontal areas involved in judging how rewarding something will feel and reining in impulses; and parts of the cingulate, tied to processing and regulating emotion.
How often someone used compensatory behaviors—which is purging behavior following a binge that clinicians currently use to rate how severe a patient's bulimia nervosa is—showed no relationship to brain structure at all. Binge eating and compensatory behaviors may therefore run on different wiring, which could eventually reshape how severity gets measured and bulimia is treated.
What this means
The study is considered "the clearest evidence to date that bulimia nervosa is associated with reproducible differences in brain structure," per Laura A. Berner, PhD, Director of the Center for Computational Psychiatry at Mount Sinai, in a press release. The location of these brain differences is what the team didn't anticipate—surface area of the outer layer is a feature largely set early in development, which raises the question of whether some of it reflects vulnerability that was present before symptoms ever started.
However, Berner drew a firm line, saying that "the findings should not be interpreted to mean that the brain is fixed, or that a person's outcome is predetermined." But rather, bulimia nervosa is a true mental illness with measurable changes, not a lack of willpower or self-control like stigma often suggests.
The takeaway
What researchers still can't say is which came first, the brain changes or the disordered behavior, because participants were scanned a single time. Still, the findings from this study give clinicians a physical thread to follow toward better prevention and treatment, and gives people living with the illness one less reason to blame themselves.
If this description of bulimia nervosa, binge-eating, or purging behavior hits close to home for you or someone you love, the National Eating Disorders Association website can point you toward treatment options in your area.