Anorexia Nervosa (AN) is an eating disorder characterised by restricted food intake and the inability to maintain an appropriate body weight. According to the National Institute of Mental Health, AN has the highest mortality rate of any psychiatric disorder, which could in part be explained by its association with excessive weight control behaviours, such as compulsive exercise and calorie restrictions . In 1983, Christopher Gillberg (a professor of child and adolescent psychiatry) began to investigate the potential link between anorexia and autism spectrum disorder (ASD), but it has since been explored by other psychologists. Although these two conditions initially appear to be vastly different from one another, research has revealed that autism and anorexia nervosa are highly co-occurring, with 20-35% of women with anorexia meeting the diagnostic criteria for autism [2, 3] . This statistic is staggering, especially when compared to the rates of autism found amongst the general population (1 in 60, according to the World Health Organisation). Given the high co-occurrence, researchers have been trying to formulate a link between the two, but there is currently no single answer as to why these two seemingly different conditions can co-occur. Here, we explore some of the major lines of thought, to try and piece together the link between autism and anorexia.
Can alexithymia explain the link between autism and anorexia?
Alexithymia may in part explain the link between autism and anorexia nervosa, due to its high prevalence in both conditions[4, 5] . Alexithymia was first introduced to psychiatry in 1972, and was defined by Sifneos as the ‘inability to recognise/describe one’s own emotions’. This lack of emotional awareness is commonly known to be present amongst the autistic community (1 in 5 autistic people have alexithymia), but it is also found in patients with anorexia (though not in all cases).
The presence of alexithymia amongst both conditions raises an important question: could alexithymia explain the high prevalence of AN amongst autistic individuals? A study by Vuillier et al highlighted this exact relationship , suggesting that alexithymia may increase the risk of eating psychopathologies in patients with autistic traits. From this, it could be implied that alexithymia acts as the link between ASD and AN, but what still remains a question is how and why alexithymia may aid the development of anorexia. For psychologists to draw stronger conclusions about the role of alexithymia in the development of AN, more research needs to be conducted.
Currently, some studies, such as the Longitudinal European Autism Project (LEAP), are investigating alexithymia’s role in several mental health disorders (especially anxiety), which may eventually help to uncover this vital link. Furthermore, Dr Oakley et al. found that difficulties in identifying feelings are significantly related to anxiety severity for some people with autism, especially women (Find article on our website here). This research, when coupled with the fact that there is such a high prevalence of mental health conditions in patients with anorexia, may eventually reveal the role of alexithymia in the development of AN.
So, though the understanding between the two are tenuous, it is important to acknowledge the possibility that alexithymia could be the missing link between ASD and AN.
Anorexia as a management technique for autism and its associated comorbidities
Other studies have suggested that for people ‘on the spectrum’, anorexia acts as a way of managing comorbid symptoms of ASD (‘comorbidity’ referring to the co-occurence of more than one disorder in the same individual). For example, 40% of young people with ASD have clinically elevated levels of anxiety, and anxiety levels amongst anorexic patients are also at a higher rate than the general population[5, 8]. From this statistical evidence, could one hypothesise that autistic people develop AN as a coping mechanism for anxiety? After all, when life feels out of control, the repetitive nature of an eating disorder could be somewhat comforting.
A 2019 article, published in Nature Neuroscience, provided further support for this theory by outlining the role of starvation in the reduction of anxiety . It was revealed that consuming less food leads to a decrease in tryptophan, which is responsible for the synthesis of serotonin (a chemical messenger that acts as a mood stabilizer ). This reduction in tryptophan and serotonin results in reduced levels of anxiety, which is a favourable response for a person with ASD who is likely to suffer from crippling anxiety on a daily basis.
Perhaps this is why some eating disorders appear to be ‘addictive’ in nature- if consuming fewer calories produces a ‘thrill’ by decreasing anxiety, it may encourage the continued restriction of food intake. From this evidence, is it reasonable to suggest that anorexia is developed as a way of managing comorbid symptoms, such as anxiety, or is this too far of a stretch? More research would need to be conducted into the other comorbid symptoms of autism (e.g. depression) to better confirm this link.
Cognitive rigidity in anorexia and autism
A link between autism and anorexia could also be examined when looking at the concept of cognitive rigidity . Sometimes referred to as ‘all-or-nothing thinking’, cognitive rigidity can be defined as the inability to mentally adapt to new demands or information. Professor Janet Treasure, a Psychiatrist at King’s College London, stated that routines, rituals and rules are ‘craved’ by people ‘on the spectrum’, as well as those suffering with anorexia nervosa , thus highlighting the overlap of this characteristic between the two conditions.
Research conducted at the Maudsley Hospital in London has specifically investigated this link. They found that both anorexic and autistic patients have a strong tendency to suffer from rigid ways of thinking and obsessive behaviours. Not only did they both display a strong resistance to change, but they also showed great attention to detail.
This evidence was developed further when Dr. Eric Hollander proposed that these ritualistic behaviours, that characterise both autism and anorexia, may actually be traced back to the same regions of the brain . If this is true, could it explain why autistic traits are more likely to be found in people with anorexia, as both conditions utilise the same regions of the brain? Alternatively, maybe it could also explain why some individuals with ASD find it easy to develop anorexia, due to their shared ritualistic/rigid behaviours.
Whether the aetiology of both conditions is the same is a different question, as more studies would need to be conducted for this specific link to be confirmed. For now though, it is interesting to consider that perhaps one area of the brain is responsible for the development of both conditions, or at least some of the traits observed in both.
Low functioning oxytocin systems in anorexic and autistic patients
Similarities between autism and anorexia can also be found by investigating the parallels between their oxytocin systems. Studies have revealed that people with ASD and people with AN show deficits in the processing of oxytocin (a hormone produced by the hypothalamus), a finding that has reinforced the link between these two co-occurring conditions. For example, one study, which examined blood samples from 29 autistic children, and 30 neurotypical children, found that the autistic group had significantly lower blood-oxytocin levels than the control group . Similarly, further research has revealed that there is a lower level of oxytocin in the cerebrospinal fluid of women with restricting anorexia .
From this evidence, one might suggest that ASD and AN are linked by their association with a low functioning oxytocin system, but not all research has arrived at this conclusion. For example, whilst some studies have revealed the role of low oxytocin levels as a potential cause of autism (oxytocin is known to impact the formation of healthy relationships, as well as the development of empathy, so if an individual is deficient in this vital hormone, they would be more likely to develop autistic traits ), other studies have found that oxytocin deficiencies may actually be an effect of anorexia : self-starvation negatively impacts the endocrine system by triggering the release of fewer hormones, including oxytocin. These endocrine changes occur after ‘prolonged starvation’ in an attempt to conserve the body’s energy and protein .
This area of research has a lot of unanswered questions, which not only makes it difficult to conclude that these two conditions are actually associated, but it also creates opportunity for further investigation. For example, to confirm that low levels of oxytocin are an effect of anorexia, one might suggest measuring oxytocin levels prior to the development of the condition, so that a comparison could be made. This isn’t realistic, because for a comparison to be made, researchers would need to conduct a longitudinal study measuring the oxytocin levels of people who are predisposed to anorexia. Although this is possible, such a study is yet to exist, so alternative solutions to this question may need to be developed.
Additionally, it could be of interest to explore whether having both ASD and AN lowers oxytocin more than one of the conditions alone.This could highlight the role of AN in actively decreasing oxytocin levels, thus removing the potential role of low oxytocin levels in the development of AN.
For now, these questions remain unanswered, but either way it is undeniable that a reduction of oxytocin may cause similar behavioural manifestations seen in both ASD and AN. What does remain a question, however, is whether the two disorders actually have the same origin.
Can the findings be criticised?
The link between autism and anorexia is undeniable, but what can be criticised is the absence of men within research samples. Perhaps the media has misled people to believe that anorexia is a ‘female dominant’ condition, but it is important to note that eating disorders do not discriminate. If men are impacted by this condition too, why are they being underrepresented in the research samples? A valid explanation for this could be found when looking at statistics. For example, although 1 in 3 people struggling with an eating disorder is male, around 2.5% of men actually suffer from AN . Therefore, if women are more likely to suffer from anorexia than men, doesn’t it make sense that they have a higher representation in research samples?
For now it remains unclear why females are more likely to develop AN, but peer pressure and the media are thought to play fundamental roles. For example, social media pressures women to obtain a certain body type, and ‘influencers’ are often seen promoting limited diets [17, 18]. Additionally, if autistic women are seen using anorexia as a coping mechanism for comorbid symptoms, such as anxiety, couldn’t this influence other women ‘on the spectrum’ to start restricting their calorie intake too? In the future, it would be beneficial to see this link being explored further- why are women more likely to suffer from anorexia than males, and are autistic women predisposed to developing such a condition?
After reviewing this evidence, it is clear that there is a link between autism and anorexia. Research has suggested that AN can be used as a coping mechanism for ASD, but it has also highlighted similarities between their biological systems, indicating that the two conditions could be linked. Now it is important to consider where research could go from here. Perhaps the first step could be to review current eating disorder treatments, which are largely inaccessible to people ‘on the spectrum’. For example, current treatments tend to involve overwhelming group settings, the need for in-person visits, and long inpatient stays that disrupt routine. Is it not wrong of health professionals to assume that people with autism will engage in conventional therapies the same as neurotypicals? Thus, an appropriate next step would be to develop a new treatment for AN that can be easily accessed by people with ASD. Additionally, perhaps mental health professionals should be educated about how the two conditions interact with one another. This requires more research to be conducted, but it is a suitable goal for the future.
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