Eating Disorders: The Brain-Gut Connection
Eating disorders are biologically-based brain illnesses that are noted by changes in food behaviors, eating, and self-perception. Eating disorders are complex illnesses that often become increasingly severe.
Over the last decade, we have seen a new area of research take shape as investigators have studied the brain, personality traits that are mediated by how the brain is wired, and how the brain processes reward. Recently, fMRI studies have demonstrated differences in the experiences of reward in individuals with eating disorders compared to controls who have never had eating disorders as well as people who had an eating disorder but are now recovered.
These studies found that people with Anorexia Nervosa experience less stimulation of the reward pathways of the brain, while people with bulimia seem to experience more active reward pathways. Early research examining reward processing in individuals with binge eating disorders shows data similar to those with bulimia. Additionally, there is emerging research on the gut’s connection to mood and brain function that may illuminate our understanding of eating disorders.
Eating Disorders and the Brain
Eating disorders are complex and can affect anyone, although they are more likely to affect individuals with specific traits. Many individuals restrict their eating, engage in dieting, or overeat, however, only some of those individuals develop an eating disorder. Why? The answer starts with an individual’s traits at a young age. If children are anxious, obsessive, perfectionistic, and achievement-driven, they seem to be more likely to develop an eating disorder. During puberty, some of these children will also undergo brain development, changing hormones, stress, and other environmental factors, which when they occur together with a change in dietary intake and/or activity can trigger the emergence of an eating disorder that, in essence, hijacks these traits.
Individuals with certain traits may engage in different eating patterns due to the pursuit of athletic achievement, appearance change, or because of an illness that alters the appetite. This new way of eating and reacting to food, such as overeating or restricting food intake, can stick in a way that most dietary changes don’t. In these situations, individuals can develop rigid eating habits, out of control eating, and/or numerous restrictions and rules around eating. Changes in eating can increase an individual’s stress level and decrease their mood and/or it can feel anxiety reducing and soothing. If perpetuated over time, this change in eating can result in biological changes that may reinforce brain patterns of rigidity, anxiety, depression, and/or impulsivity.
Given the multifactorial nature of eating disorder development, it seems that these trait-based eating disorder risk factors triggered in the context of environmental pressures on appearance, eating, and weight, weight bias, weight teasing, and individual stressors and transitions can lead to the onset of an eating disorder.
The Brain-Gut Connection
Eating behavior is mediated by a network of interacting neural circuits in the brain that includes the hypothalamus, the dorsolateral prefrontal cortex, the amygdala, the striatum, and the midbrain. In connection with these neural circuits, eating involves food intake, reward (pleasure and motivation), and satiety. When an individual is hungry, human biology compels them to seek out food. Upon eating, an individual usually feels the reward of pleasure. Upon continued eating, an individual reaches satiety and finds energy balance.
However, humans are able to override hypothalamic energy balance signals. Individuals are able to overeat despite reaching a sufficient level of energy storage. Individuals are also able to undereat, despite needing immediate and stored energy. The alterations in the brain neural circuits seen in fMRI studies indicate that people with eating disorders have different neural reactions than most people in that absence or the presence of food. There seem to be multiple dimensions to the neural reactions to eating.
It may be that the two primary dimensions at play in the brain can be described as wanting – the anticipation of getting a food reward – and liking – how the brain perceives the actual experience of getting the food stimulus. In other words, how the brain interprets the messages received during the experience.
Kent Berridge from the University of Michigan describes pleasures related to stimulus sensations that are interpreted as such by the brain. He writes, “Sensations as they enter the brain. The brain systems then must actively paint the pleasure onto the sensation to generate a ‘liking’ reaction—as a sort of pleasure gloss or varnish.” If an individual consumes a food that is enjoyable, they will experience increased activity in their GABA and opioid receptors. If they do not have a strong “liking” reaction, they may not get the expected pleasure of the stimulus, leading to distress.
Back to the wanting part of the system. Wanting is the expression of the appetitive and motivation-driven systems. Wanting is the drive individuals experience when they are motivated to seek something, like food. Wanting is a component of the reward system but not the whole system. Dopamine, the neural substrate involved in wanting, drives an individual to seek out something pleasurable. When and if the stimulus is experienced as pleasure or “liking,” the wanting system is rewarded. If the liking is dulled or absent, the expectation fueled by wanting is not met.
From this perspective, the liking and wanting systems can play directly into eating disorder behavior and experience of eating in people with eating disorders. In one fMRI study, it was noted that individuals with restrictive eating disorders experience lower levels of wanting—a decreased drive to eat. Instead of experiencing the liking sensations upon eating, these individuals often experience fear or anxiety. For those with binge eating, it seems that they have an opposite experience; they may experience a high wanting drive but a lower level of liking. These individuals may end up overeating because they experience a lower level of satiety and satisfaction upon eating.
Keep in mind that these systems do not function entirely independently and may be functioning simultaneously, one more strongly than the other or more dominantly than the other, but both may be possible. In this way, wanting may function as a “go” or a “hold on” cue and liking as a “keep going” or a “no thank you” cue.
Gut Involvement in Eating Disorders
Healthy individuals with a well-functioning central nervous system and normal gut physiology have an interplay between the two that seem to inform mood, immune function, and GI function. They have normal gut microbiota and typical levels of inflammatory cells and mediators. Those who are experiencing stress or disease often experience alterations to their behavior, cognition, and emotion, along with abnormal gut function. These variations often cause increased levels of inflammatory cells in the gut and intestinal dysbiosis (microbial imbalance or maladaptation inside the body).
Current research has increasingly linked gut microbiome status with psychiatric disorders. A study in Biological Psychiatry noted that, “Scientists say the evidence confirms that diet-induced changes can have an immediate and profound effect on brain function. The findings also suggest physicians look to diet and microbial makeup as a therapeutic target for neuropsychiatric disorders.” While this is very early stage research, there are possibilities worth exploring. This is important for those with eating disorders, where eating habits can be extreme and have an impact on the gut and gut microbiome that is potentially significant.
As an individual’s gut makeup is directly related to what they consume, it can be assumed that eating disorders can negatively impact gut health in a cyclical and/or progressive way. As eating disorders progress, individual’s guts may become increasingly stressed and gut microbiome balance may become impacted. These changes to the gut may cause changes in an individual’s hunger, desire, metabolism, and satiety upon eating. These changes can contribute to dysbiosis and they may be a factor in eating disorders, anxiety, and depression. Since gut microbiome changes occur with diet change and eating disorders significantly impact dietary patterns, the potential for gut microbiome to impact mood is under exploration.
In summary, the brain and gut interact in individuals who are living with eating disorders. Abnormal brain behaviors can reinforce abnormal gut bacteria and vice versa. These changes to the brain and gut often coexist and reinforce eating disorder behavior. In the provision of care for people with eating disorders, it is essential to consider both brain and gut function.
Eating Disorder Recovery
Due to the complex nature of eating disorders, it is important to address all aspects of eating disorders, including the brain and the gut. Oftentimes, GI discomfort, anxiety, depression and appetite changes experienced during an eating disorder cause difficulties during recovery. These difficulties may include stomach discomfort, nausea, and other uncomfortable responses to reintroducing certain foods or establishing new eating patterns.
In addition to the gut-related challenges an individual is likely to experience during recovery, it is also likely they will experience hardship when establishing healthier, restorative food behaviors. As an eating disorder progresses, patterns become reinforced and thus harder to break. When attempting to enforce new behaviors and patterns, it is common for individuals to experience distress, anxiety, fear, and depression.
While eating disorder recovery is incredibly challenging, it is possible. By receiving specialized care that is able to address all aspects of an eating disorder, individuals are likely to experience lasting recovery.
If you or a loved one is experiencing disordered eating, it is important to seek help as soon as possible. By starting eating disorder treatment early into the illness, patterns are easier to change and recovery may take a shorter period of time. While this is often true, recovery is possible for everyone—no matter how long you have lived with an eating disorder. If you are ready to start treatment, call The Emily Program today at 1-888-364-5977.
- Co-Occurring Disorders, Eating Disorders, Education, For Providers, Nutrition, Physical Health, Research