In patients with anorexia nervosa, the brain’s reward response to taste is alternatively linked with high anxiety and a drive for thinness, and this association could play a role in driving the disorder, according to a new study published in the journal JAMA Psychiatry.
Researchers at the University of Colorado Anschutz Medical Campus monitored a large group of patients with anorexia nervosa as they tasted sugar during brain imaging.
The findings show that the brain response of anorexics was higher than those in the control group, representing a biological marker for the illness. At the same time, this brain response was related to high anxiety and less weight gain in those being treated for the disorder.
As these patients restricted their diet, a brain reward circuit associated with the neurotransmitter dopamine became more active but also triggered anxiety, making food avoidance worse and perpetuating the often deadly disease.
“When you lose weight your brain reward response goes up,” said Dr. Guido Frank, MD, associate professor of psychiatry and neuroscience at the University of Colorado School of Medicine. “But instead of driving eating, we believe it elevates anxiety in anorexia nervosa, which makes them want to restrict more. This becomes then a vicious cycle.”
Using brain scans, the researchers observed 56 female adolescents and young adults with anorexia between the ages of 11 and 21 years old, and 52 healthy control participants in the same age range. All of the participants learned to associate colored shapes with either getting or not getting a sugary solution. Sometimes when they expected sugar they got nothing, and sometimes when they didn’t expect sugar they received it.
Patients with anorexia responded more strongly to the unexpected getting or not getting of sugar water, perhaps due to the release of dopamine. In addition, the greater the brain response, the greater the harm avoidance appeared to be in those with anorexia nervosa. Harm avoidance is an anxiety measure for excessive worrying and fearfulness. In these patients, it pushes the drive for thinness and furthers body dissatisfaction.
The researchers found that the higher the brain response, the lower the weight gain during treatment. This brain reward response acted on the hypothalamus, an area of the brain that stimulates eating. The team hypothesized that this could make it possible to override and fend off signals to eat.
“An enhanced dopamine reward system response is an adaptation to starvation,” the study said. “Individuals vulnerable to developing anorexia nervosa could be particularly sensitive to food restriction and adaptations of reward response during the [mid-adolescence] development period.”
According to Frank, anorexic behavior could alter brain circuits and influence the taste-reward processing mechanisms. Anorexics who are already worried about shape and weight become even more concerned. And a strong response that says “feed me” might be overwhelming and trigger even more food restriction instead of eating.
The study noted that while most people like tasting sweets, those with eating disorders associate the taste with weight gain and try to avoid it. The researchers found that brain activation among those with anorexia was inversely connected with any pleasant experience of eating sugar.
“Our data raise the possibility that adolescents with anorexia nervosa in this study were negatively conditioned to sweet taste and may have developed an inverse association with dopamine release across the larger (brain) reward circuitry,” the researchers write.
Frank believes these insights could lead to new treatments for eating disorders.
“I hope we can use these findings to manipulate these biomarkers and design better treatments for this often-deadly disease,” he said.
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