Researchers have come to the conclusion that the brains of women with bulimia respond to and process food cues in different ways than women without the eating disorder.
Writing in the Journal of Abnormal Psychology, lead author Brittany Collins, Ph.D., of the Children's National Medical Center in Washington, D.C., and colleagues suggest that their findings support the idea that binge eating serves as an escape from negative self-thoughts at times of acute stress.
People with bulimia nervosa, or simply bulimia, experience repeated and frequent bouts of binge eating that they feel they cannot control. During these episodes, they consume unusually large quantities of food, which they try to compensate for by forced vomiting, fasting, over-exercising, or using laxatives.
Over time, bulimia can take its toll on health. It can lead to a chronically inflamed sore throat, erosion of tooth enamel, stomach disorders, severe dehydration, and bowel problems. It can also result in electrolyte imbalances that raise the risk of stroke and heart attack.
It is thought that, at any one time, bulimia affects around 0.3 percent of, or 3 in every 1,000, adults in the United States, with women much more likely to have it than men.
Escape from negative self-thinking
There is a widely held working theory that binge eating helps people with bulimia to escape self-critical thinking during times of stress, allowing them, instead, to focus on something concrete and in the present, despite the fact that it can be damaging in the long-term.
In their study paper, Dr. Collins and colleagues explain how this theory is supported by several studies showing that stress and negative emotions tend to be raised before bouts of binge eating, and that negative emotions tend to decline afterward.
More recently, scientists have become interested in studying brain function to find explanations for bulimia. However, Dr. Collins' team notes that while a few studies have looked at how stress and extreme negative emotions impact the brain processing of food cues, these have not included people with bulimia - a finding that surprised them.
"To our knowledge, the current study is the first investigation of the neural reactions to food cues following a stressful event in women with bulimia nervosa," says Dr. Collins.
No difference in stress levels and cravings
For the first part of their study, the team recruited 10 women with bulimia and 10 who did not have it, and they took MRI scans of their brains as they looked at pictures of food.
Before undergoing their individual MRI scans, the participants were all given the same meal to eat. They then waited for an hour before entering the scanner.
While in the scanner, the participants were shown two sets of pictures. The first set portrayed neutral objects, including leaves and items of furniture. The second set comprised photographs of high-fat and high-sugar foods, such as chocolate brownies, ice cream, and pasta or pizza with cheese sauce.
Following exposure to the food cues, the participants were then asked to complete a task that is used in psychology experiments to induce stress and threaten the ego: a mathematical problem that is impossible to solve.
After a period of trying to complete the stressful task, the women then went back into the scanner and were exposed to a different set of food cues made up of photographs of high-fat and high-sugar foods.
After each of the three tasks - the first viewing of the food cues, the stress task, and then the second viewing of the food cues - the women were asked to rate their levels of stress and food craving.
The results showed that all participants reported similar levels of raised stress after the stress task, and similar levels of stress reduction following the second exposure to the food cues after the stress task. All participants also reported that their craving for food went up after viewing the food cues.
MRI brain scans tell different story
However, while the self-reported measures of stress and food craving were largely similar for both groups, their MRI brain scans tell a different story.
The MRI brain scans of the women with bulimia showed that as they viewed the food cues shown to them after the stress task, there was a decrease in blood flow through the precuneus, which is a brain region associated with thinking about the self. For the women without bulimia, there was an increase in blood flow through this region.
The result surprised the researchers, who were expecting to see an increase in blood flow to this region when a person is ruminating and thinking about themselves in a critical way.
The team then carried out the experiment again in another group of 17 women with bulimia. They found that the results were the same. Much like before, the women reported raised stress levels following the stress task, and increased craving for food following the food cue exposures.
And, most significantly, the MRI scans also found the same decreased levels of blood flow in the precuneus during exposure to food cues following the stress task.
The team believes that that the experiments highlight a possible mechanism in the brain that shifts attention from negative self-reflection to something concrete and in the present - namely, food cues - at times of stress for women with bulimia.
They suggest that their results should be treated as preliminary, and they call for others to confirm them with their own studies.
"Our findings are consistent with the characterization of binge eating as an escape from self-awareness and support the emotion regulation theories that suggest that women with bulimia shift away from self-awareness because of negative thoughts regarding performance or social comparisons and shift focus to a more concrete stimulus, such as food."
Dr. Brittany Collins