The role of stress in eating disorders appears to be more complex than previously thought. This is shown by a new study with bulimia and anorexia patients. Contrary to popular theories, stress did not change the test subjects’ ability to solve self-control tasks. Their eating behavior was also unaffected by stressful situations. However, brain scans showed that certain regions that are involved in self-control are activated differently in people with eating disorders.
Binge eating is a characteristic symptom of various eating disorders, including bulimia and certain forms of anorexia. In many cases, excessive food intake is followed by deliberately induced vomiting. In such situations, those affected often experience eating as an uncontrolled process in which they have the feeling that they cannot stop their current action. So far, scientists have assumed that so-called binge eating is a result of stress that leads to difficulties with self-control in those affected.
Disturbed self-control under stress?
A team led by Margaret Westwater from the University of Cambridge has now tested this theory on patients for the first time. “Our results show fascinating changes in stress responses and inhibitory functions associated with binge eating, but they make it clear that stress-related failures in inhibitory control are not a sufficient explanation for uncontrolled eating,” the researchers write.
For their study, they examined 85 young women, 22 of whom were anorexic, 33 with bulimia and 30 control persons without an eating disorder. The test subjects spent two days in the research institute, during which their food intake was monitored. After a set breakfast, they completed an inhibitory self-control task. On a screen they saw a growing bar that they should stop with the push of a button as soon as it crossed a line on the screen. In some cases, however, the bar stopped prematurely by itself, so that the test subjects had to suppress their impulse to press the button. During this time, their brain activity was recorded with functional magnetic resonance imaging (fMRI).
Different reactions in the brain
After this first round of experiments, the researchers deliberately put some of the test subjects under stress: They had to solve mental arithmetic problems and repeatedly received light but unpredictable electric shocks. In addition, the researchers told them that if they did not do the tasks well enough, they would be excluded from the study and gave them feedback that their performance was below average. After this stressful situation, the test subjects should complete the task with the bar again. Since inhibiting self-control is crucial in this task, according to the current theory, it would have been expected that the stressed test subjects would do worse.
To the researchers’ surprise, however, stress did not affect performance in either bulimia or anorexia patients or controls. However, brain activity actually differed depending on whether the test subjects were stressed or relaxed – in different ways depending on the eating disorder. The brain of women with bulimia showed increased activity in the superior frontal gyrus (SFG), a region in the prefrontal cortex that is involved in self-control. In contrast, other brain regions, including the premotor cortex, were less active. “These stress-induced increases in SFG activity may have compensated for the simultaneous decrease in premotor activity, which meant that task performance was maintained,” the researchers suggest. Overall, however, the bulimia patients showed the worst performance in the bar exercise regardless of their stress level.
In contrast, the activity in the prefrontal cortex was reduced in anorexic patients. “This could reflect the consequences of long-term, extreme stress, triggered by a significantly low weight, which causes various cognitive and neuroendocrine disorders,” the researchers say.
Direct effects on eating behavior tested
In order to additionally record the direct effect on eating behavior, the research team offered the women an all-you-can-eat buffet after completing the tasks and said they could eat as much or as little as they want. The women who had previously gone through the stress task were still in a state of stress at this point in time – and thus, according to previous theories, more susceptible to uncontrolled binge eating. Nevertheless, none of the test subjects showed excessive eating behavior. Overall, the persons with eating disorders consumed fewer calories at the buffet than the control persons. However, the researchers cannot rule out that the unfamiliar environment and the observation made eating attacks less likely than they would have been under natural conditions.
“Our work makes it clear that the relationship between stress and binge eating is very complicated,” says Westwater’s colleague Paul Fletcher. “It’s about the environment around us, our psychological state and how our body signals to us that we are hungry or full. To help people with eating disorders, we need to take a holistic approach to research into these diseases. “
Source: Margaret Westwater (University of Cambridge, UK) et al., Journal of Neuroscience, doi: 10.1523 / JNEUROSCI.2853-20.2021