Impaired proactive inhibition in bulimia nervosa is associated with increased activity of the upper frontal gyrus. Photo credit: Westwater et al., JNeurosci 2021
A unique residential study found that contrary to the perceived wisdom, people with eating disorders do not lose self-control – which leads to binge eating – when responding to stress. The results of the Cambridge-led research are published today in the Journal of Neuroscience.
People who develop bulimia nervosa and a subset of those with anorexia nervosa have certain key symptoms, namely recurring binge eating and compensatory behaviors such as vomiting. The two diseases differ largely in terms of their body mass index (BMI): adults who are affected by anorexia nervosa tend to have a BMI of less than 18.5 kg / m2. More than 1.6 million people in the UK are believed to have an eating disorder, three quarters of whom are women.
A prominent theory of binge eating is that it is a result of stress that causes people to have difficulty controlling themselves. So far, however, this theory has not been tested directly on patients.
To investigate this theory, researchers from Cambridge University, in collaboration with clinicians in Cambridgeshire and the Peterborough NHS Foundation Trust, invited 85 women – 22 with anorexia nervosa, 33 with bulimia nervosa and 30 healthy controls – to a Trust-MRC for a two-day stay at Wellcome Institute for Metabolic Science Translational Research Facility (TRF). The facility, which includes an eating habits department, is designed so that a volunteer’s diet and environment can be tightly controlled and their metabolic status examined in detail during a residential status. The setting should be as naturalistic as possible.
During their stay, the women received controlled meals provided by a nutritionist every morning. The women then went through a Lent during which they were taken to the Wolfson Brain Imaging Center next door, where they performed tasks while their brain activity was monitored with a functional MRI scanner.
The first tasks were to stop the progression of a bar displayed by pressing a button on a computer screen. The main task was to stop the moving rod when it reached the center line. In a minority of attempts, stop signals have been presented in which the moving beam automatically stopped before it reached the center line. Participants were instructed to withhold their response in the event of a stop signal.
The women then performed a task aimed at increasing their stress levels. They were asked to perform a series of mental arithmetic tests while receiving mild but unpredictable electric shocks and were told that their data would be excluded from the study if they did not meet the performance criterion. You received feedback throughout the assignment, such as: B. “Your performance is below average”.
The women then repeated the stop signal task again.
After the assignments were done – but although the volunteers were still expected to be in an increased state of stress – they returned to the Eating Behavior Department, where they were served a buffet in their relaxing lounge entitled “All That You can eat ”was offered saying they could eat as much or as little as they wanted.
On the second day of their study, the volunteers performed the same tasks, but without the added stress of unpleasant electric shocks and pressure to perform. (For some participants, the order of the days was reversed.)
Dr. Margaret Westwater, who led the research during her PhD. The student in the Department of Psychiatry at Cambridge said, “The idea was to see what happened when these women were stressed. Has it affected, and in turn increases, key areas of the brain that are important for self-control the food intake? What we found surprised and contradict the prevailing theory. “
The team found that even when women with bulimia nervosa weren’t stressed, they performed worse on the main task because they had to stop the rising bar when it reached the middle bar – but this was not the case with women affected by anorexia the nervosa case. This impairment occurred along with increased activity in one region in the prefrontal cortex, which the team said could mean these particular women were unable to recruit some other regions that the brain needs to do the best possible job.
Interestingly, and contrary to theory, stress had no effect on actual performance, neither for the patient groups nor for the controls. However, the patient groups showed some differences in brain activity when they were stressed – and this activity differed between women with anorexia and women with bulimia.
While the researchers observed that the patients generally ate less at the buffet than the controls, the amount they ate did not differ between the stress and control days. However, activity levels in two key regions of the brain were linked to the amount of calories consumed in all three groups, suggesting that these regions are important for nutritional control.
Dr. Westwater added, “Although these two eating disorders are similar in many ways, there are marked differences at the brain level. Women with bulimia, in particular, seem to have a problem with slowing down preventively in response to changes in their environment we believe they could lead to hasty decisions, making them in some way prone to binge eating.
“The theory is that these women should have eaten more when they were stressed, but we really didn’t find that. When we think about eating behavior in these disorders, we have to take a more nuanced approach.”
In the results published last year, the team took blood samples from women as they performed their duties to examine metabolic markers that are important in making us feel hungry or full. They found that levels of these hormones are affected by stress.
When under stress, patients with anorexia nervosa had spikes in ghrelin, a hormone that tells us when we are hungry. But they also had an increase in the peptide tyrosine tyrosine (PYY), a satiety hormone. In other words, when they are stressed, people with anorexia nervosa produce more hunger hormone, but also inconsistently more hormone to tell them they are full, so their bodies send them confusing signals about what to do with food.
The situation with bulimia nervosa was again different: while the team did not find any differences in ghrelin or PYY levels, they saw lower levels of cortisol, the “stress hormone”, than in healthy volunteers. In times of acute stress it is known that people who are chronically stressed or suffer from depression show this paradoxical phenomenon with low cortisol levels.
Professor Paul Fletcher, co-lead author in the Department of Psychiatry, said, “Our work shows that the relationship between stress and binge eating is very complicated. It’s about the environment around us, our mental state, and how our bodies signal us that we are hungry or full.
“If we can gain a better understanding of the mechanisms behind how our gut affects these higher-order cognitive processes related to self-control or decision-making, we may be better able to help people affected by these extremely debilitating diseases So we need to take a much more integrated approach to studying these diseases, and this is where facilities like Cambridge’s new translational research facility can play an important role in allowing us to assess factors such as an individual’s behavior and hormone levels in a relatively naturalistic setting monitor and brain activity. ”
Deciphering the Genetics Behind Eating Disorders
Westwater, ML et al. Prefrontal responses during proactive and reactive inhibition are differently influenced by stress in anorexia and bulimia nervosa. Journal of Neuroscience; April 12, 2021; DOI: 10.1523 / JNEUROSCI.2853-20.2021 Provided by the University of Cambridge
Quote: Stress does not lead to a loss of self-control in the case of eating disorders (2021, April 12), published on April 12, 2021 from https://medicalxpress.com/news/2021-04-stress-loss-self-control-disorders. html
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