Food for Thought: The Connection Between Eating Disorders and the Brain
Published Jul 25, 2012
More than 10 million people in the U.S. battle an eating disorder such as anorexia or bulimia, according to the National Eating Disorders Association. And many, many more – approximately 1/3 of all Americans – are afflicted with a type of disordered eating at the other end of the spectrum: obesity.
In anorexics, an obsession with being thin leads to severely limited food intake, often to the point of starvation and death. People who are obese (defined as having a body mass index of 30 or higher) are afflicted with excessive calorie consumption relative to their physical activity levels, and often don’t know when to stop eating.
It’s clear that at the center of these serious medical conditions is food and the ability (or inability) to control one’s intake. But issues with food are merely a manifestation of a deeper, more complicated problem. The causes of eating disorders are anything but simple. But we do know that chemicals in the brain and nervous system play a significant role in what drives people to eat too much, or not enough.
Here’s what we do know, and what we’re just starting to find more about.
Neurochemicals that drive disordered eating
Many studies have shown that the fluctuation of dopamine and serotonin levels, two major chemicals that affect mood and appetite, are not normal in those with eating disorders. How that plays out in their eating habits, though, is still unclear.
Dopamine is a neurotransmitter that controls the feeling of pleasure and reward. We know that the positive, satiated feeling one gets after eating is partially due to increased dopamine levels; it’s the reward after the so-called “hunt,” to borrow a term from mankind’s hunter-gatherer days. But a study last year found that anorexics felt extremely anxious after a dopamine spike, which could explain why they have such an intense fear of eating.
Dopamine’s cousin, serotonin, regulates mood, including anxiety, and appetite. Several studies have found that people with eating disorders have decreased levels of serotonin. As a result, selective serotonin-reuptake inhibitors (SSRI) medications, such as fluoxetine, are often prescribed as part of a broader treatment plan. Fluoxetine is the only drug approved by the U.S. Food and Drug Administration to treat bulimia nervosa.
Anorexia, obesity may be opposite sides of the same coin
Two recently published studies, both in the medical journal Neuropsychopharmacology, add an interesting new nuance to the current body of research on eating disorders and the brain.
In one study, the subjects were divided into various groups, including a healthy control group, people suffering from anorexia, and people who were obese. After a period of fasting, researchers showed each test subject various pictures of food. Using brain imaging techniques, they found that the obese group had a high response rate in the brain regions associated with hunger and emotional reactions to food, while those with anorexia exhibited low brain activity. The study’s lead researcher, Laura Holsen, said in an interview that this suggests brain activity may have a direct effect on people eating either way too much or too little.
In the other study, researchers conditioned participants – who were either obese or anorexic – to associate sweet and non-sweet flavors with certain shapes that were shown to them. For example, they would taste a sugar water solution every time an orange circle was shown, but a neutral solution following a blue triangle. Sometimes, however, the rule was broken, so participants occasionally received a sugar solution following the blue triangle. The study’s authors found that an unexpected sweet-tasting solution resulted in increased neural activity in the brain reward circuits of the anorexic patients, but decreased neural activity in the obese group. This suggests that food triggers a more heightened reward response in people with anorexia, while those who are obese do not feel as stimulated – and so perhaps require more of it to get the same feeling of reward.
With all the research into the brain’s role in the development and recovery from disordered eating, we do know one thing for certain: Eating disorders are a complex condition with countless manifestations, and are both a psychological and physiological disease. That we now know more about the brain’s role is an important step toward preventing and treating them effectively.
Mind your health,
Dr. Keith Black