Neuroscience is an area of research that explores brain communication (i.e. how cells “talk” with each other) with the goal of understanding our thoughts, behaviours, and bodily functions.
Like a text message, brain cells send chemical messages to other brain cells that tell our body what it needs (e.g. sleep), how we feel (e.g. sad), and what we worry about (e.g. weight gain). This information influences our thoughts, actions, and health.
Understanding how the brain influences our thoughts and behaviours is important because, if we know how the brain functions during illnesses (e.g. eating disorders), we can develop better preventative measures and treatments for people who have them. Neuroscience research can also help to justify the need for care, as it can demonstrate that eating disorders benefit from medical treatment.
Studying eating disorders from a neuroscience perspective, however, is challenging. The brain is constantly changing, and there’s still a lot we don’t know about it. Also, every brain is different. This makes it difficult to determine neurobiological causes for eating disorders.
One way that researchers determine neurobiological causes for eating disorders is by seeing if eating disorder symptoms (e.g. high anxiety) are still present in recovered individuals. The rationale is that, if the symptom is present even when the eating disorder is not, that symptom is likely to have been around before the eating disorder (i.e. may have caused the eating disorder).
One cause for eating disorders is negative thinking . It has been shown that people with eating disorders have negative thoughts more frequently than people without eating disorders [2; 3; 4], and that eating disorder behaviour (e.g. binge eating or food restriction) follows negative thinking (e.g. negative social comparisons and self-evaluations [4; 1]. This is true across most types of eating disorders (e.g. bulimia, orthorexia,[5; 6] anorexia, atypical anorexia,[7; 8] and binge eating disorder).
People with eating disorders have frequent negative thoughts because, as brain studies show, they focus on threatening information (e.g. weight or food) more often than people without eating disorders [9; 10; 11; 12]. Frequent negative thinking contributes to eating disorder onset by increasing stress on the body, which changes how the brain functions. For people with eating disorders, frequent negative thinking might lead to biological changes that make coping with negative thoughts especially difficult .
Eating disorder behaviour (e.g. binge eating) can present as a coping mechanism for negative thinking . For example, for people with bulimia or binge eating disorder, binge eating might be a way for them to briefly escape negative thoughts [15; 16]. This is because, as brain imaging studies show, people who develop bulimia or binge eating disorder are motivated to eat for different reasons than people who don’t binge eat .
In contrast, food restriction might be a coping strategy for people with anorexia. This is because the body’s chemical hunger messenger, ghrelin, can also reduce anxiety [18; 19]. When people without anorexia restrict their food intake, ghrelin is sent to the brain to tell them that they need to eat. When people with anorexia restrict their food intake their brains receive a lot more ghrelin than people without anorexia [20; 21]. Therefore, restricting food intake can reduce anxiety for people with anorexia.
Brain scans also show that people with anorexia symptoms find high-calorie foods less rewarding than people without anorexia symptoms; this could be due to how their brains communicate information about food reward [22; 23]. It’s unclear, though, if increased ghrelin signalling causes anorexia or if it’s a consequence of malnutrition [24; 25].
Changes in brain chemicals, such as serotonin, also contribute to eating disorder onset by shaping our personalities . Differences in personalities contribute to the development of different eating disorders .
Neuroscience research shows that high levels of serotonin cause personality traits common in anorexia (e.g. perfectionism, anxiousness, rigidity, and compulsivity) [27; 28; 29]. Consequently, having high levels of serotonin increase the likelihood that someone will develop personality traits that cause anorexia .
People with bulimia nervosa or binge eating disorder, in contrast, have lower serotonin levels than people without these disorders . Low levels of serotonin have been associated with personality traits common in eating disorders that include binge eating (e.g. high impulsivity and low mood) [27; 31]. This suggests that low levels of serotonin increase an individual’s risk of developing personality traits that cause one of these disorders.
Because these serotonin differences are present in recovered individuals and might have a genetic component [30; 32], differences in serotonin levels are likely to be a cause, rather than a consequence, of eating disorders .
Neuroscience can also explain body image concerns in eating disorders. People with anorexia symptoms overestimate their body size more often than people without these symptoms . Neuroscientists think that this is because their brains “talk” about their bodies in ways that favour negatively biased self-references [34; 35]. These body overestimations persist in recovery and, therefore, might contribute to eating disorder onset .
People with eating disorders also struggle with bodily cues in ways that contribute to eating disorder development. Bodily cues are internal messages that inform people about the state of their bodies (e.g. when they are hungry). Listening and responding appropriately to these cues (e.g. feeling hungry and eating) is called “interoceptive awareness” .
People of all weights with most eating disorder types have low interoceptive awareness [22; 38] This means they can’t accurately recognise when they are hungry, full, or experiencing certain emotions. For example, people with avoidant/restrictive food intake disorder (ARFID) receive fullness cues sooner during a meal than people without ARFID . This prevents them from relying on their bodies to know when to stop eating. Low interoceptive awareness can be both a cause and consequence of an eating disorder [40; 41].
Poor gut health also contributes to eating disorder onset by influencing our thoughts and behaviours [42; 43]. Scientists are only just beginning to understand how the gut causes mental illness and, consequently, few studies have explored its role in eating disorders. One study found that people with anorexia have a gut low in bacterial diversity, which might reduce interoceptive awareness . Less is known about how the gut might cause other eating disorders, though gut discomfort is a known cause for ARFID .
Childhood gut discomfort is a known cause for ARFID, as the unpleasantness of eating can lead to food restriction and aversions to hunger and fullness cues (i.e. poor interoceptive awareness). Additionally, bad (e.g. choking) and unpleasant sensory experiences (e.g. dislike of certain textures) with food can cause ARFID . These sensory experiences in ARFID overlap with autism . The brains of people with ARFID, like those of people with autism, might be biased to communicate unpleasant information about food texture, smell, colour, and taste . Because so much brain development happens during childhood, these early life experiences with food (e.g. food avoidance) shape future eating behaviour, which can include the development of ARFID.
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