that we understand the contributing factors and develop new
Circuits gone awry
Broadly speaking, eating disorders are any illnesses that cause
serious disturbances to one’s diet. These disorders include the
relatively well-known anorexia, characterized by extreme food
restriction and emaciation, and bulimia, marked by episodes of
binge eating followed by purging, fasting or excessive exercise.
At the opposite end of the spectrum from anorexia is binge-
eating disorder, in which people experience insatiable cravings
that cause them to eat large amounts of food beyond mere
“overeating.” Still other eating disorders fall into a catchall
category known as “eating disorders not otherwise specified.”
What all of these disorders share is a dangerously
maladaptive approach to food.
Unsurprisingly, binge-eating disorder is often associated
with obesity. People with anorexia and bulimia, on the other
hand, fear gaining weight. Anorexia and bulimia often arise
during the teen or early adult years, and are more common
among women than men. According to a study by James
Hudson, MD, ScD, and colleagues, 0.9 percent of women and
0.3 percent of U.S. men develop anorexia during their lifetime,
while 1. 5 percent of women and 0.5 percent of men develop
bulimia (Biological Psychology, 2007).
Untreated, bulimia can lead to serious illnesses including
gastrointestinal problems, electrolyte imbalance and
cardiovascular disease. Anorexia can cause muscle wasting,
heart and brain damage, and multiorgan failure. Indeed,
anorexia has been reported to have one of the highest mortality
rates of any psychiatric disorder.
“There are many disorders that are maladaptive, but in
anorexia, individuals are basically starving themselves to death,”
Zucker says. “You don’t have to be a scientist to step back and
say there’s something horribly wrong here.”
While anorexia and bulimia both have distinct features, the
disorders appear to share some biological underpinnings. Both
are highly heritable, for example. But while one family member
might develop anorexia, another will experience bulimia. And
it’s not uncommon for someone with one of the disorders
to later develop the other. “That points to some common
vulnerability — possibly neurological vulnerabilities,” Zucker
People with anorexia and bulimia also tend to have relatively
“When they’re children, before the onset of an eating
disorder, these tend to be kids [who] are anxious, obsessive,
perfectionistic and achievement-oriented,” Kaye says.
Yet eating disorders are more complicated than a
perfectionist temperament gone awry. A faulty reward-
processing system seems to be an important feature of the
diseases. Learning from rewards is an ancient ability across
the animal kingdom, and the process is particularly potent in
guiding eating behaviors. When we eat a bite of chocolate cake,
we’re rewarded with the pleasure of its taste, and want to take
That basic process breaks down in anorexia, Kaye says.
“There’s an altered balance in people with anorexia where
they have difficulty coding reward, and they’re oversensitive to
In one demonstration of this breakdown, Kaye and
colleagues scanned the brains of healthy women and women
with anorexia as they played a monetary betting game. In
women with anorexia, brain circuits involved in reward
processing were less active when they won, but more active
when they lost (Psychiatry Research: Neuroimaging, 2013).
An important piece of the altered reward system seems to
be dopamine, the neurotransmitter that motivates us to cut
a second helping of that chocolate cake. Dopamine activity
is altered in both bulimia and anorexia — but in opposite
ways, according to research by Guido Frank, MD, a professor
of psychiatry at the University of Colorado Anschutz Medical
Women with bulimia have a weaker-than-normal response
in brain regions that are part of the dopamine-related reward
circuitry, while the reward circuits in women with anorexia are
overly sensitive to food-related stimuli, as Frank described in a
recent review (CNS Spectrums, 2015).
For most people, eating is an enjoyable activity. People with
anorexia, though, often report that sitting down to a meal
makes them feel worried — and there appears to be a biological
reason for that reaction. Kaye and colleagues have found that
in people with anorexia, the release of dopamine in the dorsal
striatum triggers anxiety rather than pleasure (International
Journal of Eating Disorders, 2012).
As scientists delve into the faulty reward system, they’ve
identified several brain regions that are possible perpetrators.
One is the orbitofrontal cortex, which is involved in signaling
us when to stop eating. Research has found that people with
anorexia and bulimia have structural and functional differences
in this area, Frank says.
Women with anorexia also appear to have more activity in
the dorsal striatum, the brain area linked to habitual behavior,
according to New York University psychologist Karin Foerde,
PhD, and colleagues who scanned the brains of anorexic and
healthy women as they decided what to eat. (Because anorexia is
much less common in men, most research focuses on women.)
Traditionally, people with anorexia have often been thought
of as having formidable willpower, allowing them to avoid food
even when they’re starving. Foerde’s study suggests maladaptive
eating behaviors may have more to do with habit than with
willpower, the authors say (Nature Neuroscience, 2015).
The brain region known as the right insula also seems to
be altered in people with anorexia. That bit of brain helps to