Misread Hunger Signals May Cause Eating Disorders, Landmark Study Finds

Anorexia and bulimia are the two most well known eating disorders in the U.S., and until 2013 they were the only two eating disorders recognized by the American Psychiatric Association. For a long time, doctors and researchers have tried—with only partial success—to uncover the underlying causes for the onset of anorexic and bulimic eating behaviors. The authors of a new study, published in June 2013 in the American Journal of Psychiatry, may have discovered a new underlying contributor to these behaviors: abnormal function in the part of the brain responsible for coordinating taste input from the tongue with the ability to accurately gauge one’s current level of appetite.

Potential Anorexia Causes

People affected by anorexia develop severely dysfunctional eating behaviors as a result of several main psychological factors, including loss of the ability to accurately perceive their body size and body image, an entrenched and illogical belief that they weigh much more than they should, a fixation on getting thin enough to meet their irrational expectations, and an extreme fear of failing to meet those expectations. Most individuals with the disorder express these misperceptions and obsessions by consistently and heavily limiting their daily food intake. However, some affected individuals also periodically drop their food restrictions and engage in limited episodes of food binging. Doctors and researchers have not pinpointed a specific cause for the development of the psychological factors that drive anorexic behavior, the Mayo Clinic notes. Current theory holds that the condition probably stems from several overlapping causes. The list of potential causes at work in any given individual includes perfectionist or obsessive-compulsive personality traits, genetically inherited alterations in brain function or personality formation, chemical imbalances in the brain, and social influences such as peer pressure, celebrity worship, and a culture-wide preoccupation with notions of thinness.

Potential Bulimia Causes

People with bulimia also have psychological problems that contribute to a severely dysfunctional relationship with issues related to body weight, body shape, food and eating. The main outward manifestation of these problems is periodic participation in food binges that feature extremely high calorie intake. In the classic form of the disorder, affected individuals try to counteract the effects of these binges by purging recently consumed calories through vomiting or the use of enemas, laxatives or diuretics. In another form of the disorder, called non-purging bulimia, affected individuals attempt to prevent weight gain by doing such things as exercising heavily, undertaking food fasts, or imposing rigorous dietary restrictions between binges. As is true with anorexia, doctors and researchers believe that bulimic eating patterns likely result from the overlapping influence of a number of underlying causes. Potential contributing factors in any given case of the disorder include a family history of bulimia, personality traits that emphasize self-criticism or poor impulse control, genetic predisposition, chemical imbalances in the brain, extraordinary stress, a personal history of rape or physical assault, and the same cultural and social influences that promote the onset of anorexia.

New Findings

In the study published in the American Journal of Psychiatry, a team of researchers from UC San Diego used an imaging technology called fMRI (functional magnetic resonance imaging) to examine the brains of 28 women who had been successfully treated for anorexia or bulimia. For comparison’s sake, the researchers also used the same technology to examine the brains of 14 women unaffected by either anorexia or bulimia. During the study, all of the women were given small doses of sugar just prior to their fMRI scans in order to activate the brain processes for taste and hunger. After reviewing the fMRI results, the authors of the study concluded that, when compared to women without an eating disorder, women with a history of anorexia have an unusually low level of responsiveness in the part of the brain that coordinates the sense of taste with one’s perceived level of hunger. Conversely, women with a history of bulimia have an unusually high level of responsiveness in this same brain area. The authors believe that lack of normal responsiveness in people with anorexia may indicate a reduced ability to pick up on the body’s hunger signals. They also believe that excessive responsiveness in people with bulimia may indicate an overly amplified sensitivity to the same signals; in turn, these brain changes may act as previously unidentified core causes of the onset of anorexic and bulimic eating behaviors. The UCSD researchers said that identifying abnormal neural substrates could help to reformulate the basic pathology of eating disorders and offer new targets for treatment. “It may be possible to modulate the experience by, for example, enhancing insula activity in individuals with anorexia or dampening the exaggerated or unstable response to food in those with bulimia,” said Walter H. Kaye, author of the research. Studies indicate that healthy subjects can use real-time fMRI, biofeedback or mindfulness training to alter the brain’s response to food stimuli. For patients with anorexia who have an overly active satiety signal in response to palatable foods, the researchers suggest bland or even slightly aversive foods might prevent the brain’s overstimulation. Medications may also be found that enhance the reward response to food, or decrease inhibition to food consumption in the brain’s reward circuitry.

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