Dysbiosis, or microbial imbalances in the gut, is linked with anorexia nervosa. Despite some inconsistencies in the literature, anorexia nervosa patients have been found to have reduced gut microbial diversity compared to healthy controls, characteristic of dysbiosis and often found in other illnesses such as obesity and inflammatory bowel diseases. Low diversity in the gut ecosystem is associated with depression, anxiety, and other eating disorder psychopathology among anorexia nervosa patients, although this is likely dependent on greater severity since this relationship was not found among subthreshold healthy controls. Patients have also been found to display increased levels of Enterobacteriaceae species, such as E. Coli in stool samples as the gut environment favors pathogenic bacterial species to alter the diet of the host. Although it is unclear in dysbiosis causes or results from anorexia nervosa, there is nonetheless a clear connection between the disorder and the gut microbiome. 

Dysbiosis in Anorexia Nervosa

Some gut microbiota adaptations to starvation are adaptive, but others are counterintuitive and damage the host by reinforcing complicating factors of anorexia nervosa like metabolic dysregulation and comorbidities. With rapid diet changes, starvation, and food scarcity, microorganisms that can thrive in harsh environments with limited calories tend to thrive, and these microorganisms may contribute to the disorder's maintenance by influencing weight regulation and behavior. While further study is needed, mouse studies transplanting germ-free mice with stool samples from healthy controls and from children with acute protein-energetic malnutrition have indicated potentially causal relationships between the gut microbiome and body weight regulation, as those transplanted with the ill children's stool faced metabolic abnormalities and lost significant weight. Methanobrevibacter smithii (M. smithii), methanogenic archaeon was found to be increased in anorexia nervosa patients, with greater abundance being inversely associated with BMI. While methanogens optimize bacterial fermentation and energy extractions, high levels of M. smithii also cause slowed intestinal transit, which can contribute to constipation and complicate weight restoration efforts. 

Gut Microbiota Adaptations to Starvation

While it is still unclear if dysbiosis causes or results from AN pathophysiology, new evidence from mouse studies has indicated potential causality between microbiome changes and traits of anorexia nervosa. Germ-free mice transplanted with anorexia nervosa patient microbiota (gAN) gained less weight and had poorer food efficiency compared to mice transplanted with healthy control microbiota (gHC). gAN were found to have more Clostridium and Bifidobacterium genera compared to gHC. congruent with abnormalities found in human patients. gAN were also found to display more anxious and compulsive behaviors, inversely associated with Bacteroides fecal abundance and brainstem 5-HT levels, which were lower in gAN than in age-matched gHC. However, this compulsivity was treatable with probiotic treatment of B. vulgatus, as patients often have decreased abundance of the Bacteroides fragilis group.

Microbiome-Based Anorexia Nervosa Symptom Mechanisms

Microbiome-based interventions and information may help to inform and supplement nutritional rehabilitation in anorexia nervosa treatment, so as to alleviate problems that occur in refeeding such as gastrointestinal issues, weight relapse, etc.. Existing refeeding regimens have not been found to restore normal levels of intestinal bacterial diversity despite weight restoration, possibly indicating dysbiosis as having a role in relapse following weight restoration. Fecal microbiota transplantation (FMT), in which microbiota from healthy donors are transplanted into patients to help re-establish microbiota diversity and improve nutritional restoration has recently been found to improve gut barrier function, microbiota diversity, and weight gain in anorexia nervosa patients. However, further evidence and research is needed to establish what constitutes a "healthy" microbiota profile and establish means of improving the likelihood of compatibility between donors and recipients. Probiotics are also being studied as adjuncts to standard treatment to non-invasively improve the gut microbiome and address certain comorbidities, as some orally-taken bacterial strains have been found to improve mood and gastrointestinal function.

Microbiome-Based Interventions in Anorexia Nervosa

The gut microbiome is a diverse, abundant microbial ecosystem that helps modulate homeostasis via a symbiotic relationship with its host. It has implications in multiple complex diseases by facilitating interactions between genes and the environment, but it is vulnerable to chronic environmental disturbances, such as the dietary fluctuations and nutritional deprivation inherent to anorexia nervosa. It is likely involved in AN pathophysiology by affecting energy metabolism, intestinal permeability, immune function, appetite, and behavior, but complicated by genetic risk factors, eating patterns, etc.. Intestinal bacteria may be involved in appetite and weight regulation along with comorbidities such as mood changes and gastrointestinal symptoms by acting on metabolic, neuroendocrine, and immune pathways.

- Dysbiosis in anorexia nervosa 
- Gut microbiota adaptations to starvation 
- Microbiome-based anorexia nervosa symptom mechanisms 
- Microbiome-based interventions for anorexia nervosa

Kalamazoo College

Anorexia nervosa is an eating disorder defined by maintaining a body weight significantly below average, which is achieved through methods like starvation or excessive exercise. A central characteristic of this disorder is a distorted body image, a form of body dysmorphia, where individuals perceive themselves as overweight despite being underweight.

Anorexia Nervosa

Ghenciulescu, A., Park, R. J., & Burnet, P. W. (2021). The gut microbiome in anorexia nervosa: Friend or foe? Frontiers in Psychiatry, 11, 611677. https://doi.org/10.3389/fpsyt.2020.611677

The Gut Microbiome in Anorexia Nervosa: Friend or Foe?

Dialectical behavior therapy (DBT) has been shown to be effective in treating anorexia nervosa (AN), as patients with the disorder who underwent DBT saw low dropout rates and increased BMIs which were sustained 6 months later. While standard DBT has been shown to be effective, a DBT program that was augmented to focus on overcontrolled emotions and behaviors which contribute to AN was more helpful in encouraging long term results.

Dialectical Behavior Therapy as Treatment for Anorexia Nervosa

While there is a long tradition of studying health inequalities between social classes, the standard approach does not apply for anorexia. The intersection of the social relations of age, gender, and social background, with which they are related, accounts sociologically for the disparities in the frequency of EDs.


Anorexia in Social Relationships

Diagnostic Criteria for Anorexia Nervosa (DSM-V)

1. The individual restricts their consumption of food such that it is significantly lower than their body's energetic demand, resulting in a dramatic reduction in body weight. This reduction is evaluated in reference to the individual's expected weight, which itself varies according to their age, sex, and developmental trajectory.

2. The extreme fear of gaining weight and/or subcutaneous fat, which prevents weight restoration and/or maintenance of a healthy weight.

3. The distortion of the individual's body-image due to the their perception their body's weight or shape, low sense of self-worth because of their body's weight or shape, or the absence of an acknowledgment that their body weight is lower than what is clinically considered to be healthy.

Diagnostic Criteria for Anorexia Nervosa (DSM-V)

Research unfortunately indicates that anorexia nervosa treatment outcomes are not always ideal. Although oftentimes significant weight is restored by the end of treatment, psychological symptoms frequently go largely unaddressed, indicating a gap in current treatment procedures that may leave patients more vulnerable to relapse.

Anorexia Nervosa Treatment Outcomes

A model explaining the intra- and inter-personal maintenance factors for the continued duration of anorexia nervosa, not bound by Western sociocultural limitations. Intrapersonal factors combine to predispose individuals to anorexia nervosa and contribute to its maintenance, eliciting strong reactions from close others which then create interpersonal factors that further perpetuate the illness:

- Perfectionism/cognitive rigidity
- Experiential avoidance
- Pro-anorectic beliefs
- Expressed emotions

Cognitive-Interpersonal Maintenance Model of Anorexia Nervosa

Individuals diagnosed with anorexia nervosa will typically have a distorted body image, which refers to when one feels they look overweight despite not being overweight. Distorted body image is a type of body dysmorphia.

Distorted Body Image

Anorexia Nervosa and the Gut Microbiome

Individuals with anorexia nervosa face an elevated risk of developing other psychological problems. Commonly co-occurring conditions include anxiety disorders, mood disorders, and issues with substance abuse.

Psychological Comorbidities of Anorexia Nervosa

The prevalence of anorexia nervosa is estimated to range from just under 1% to over 4% among women. The rates of this disorder are significantly lower for men.

Prevalence of Anorexia Nervosa

An example of a public health initiative is an Italian advertising campaign that was created to increase public awareness about anorexia nervosa. This campaign was highlighted in a news story to broaden its reach.

Italian Advertising Campaign for Anorexia Nervosa Awareness

A 19-year-old student is brought in for a consultation by her concerned parents. She is 5'7" tall and weighs 98 pounds. Despite her significantly low body weight, she expresses an intense fear of gaining weight and frequently states that she feels 'fat,' often pointing to her stomach and thighs. Her parents report that she eats very small portions, avoids high-calorie foods entirely, and engages in a rigorous two-hour exercise routine every day. Based on this information, which psychological disorder is most likely being described? Justify your answer by identifying at least two key features from the scenario that align with the typical presentation of this disorder.

Clinical Scenario Analysis

The medical consequences of anorexia nervosa are primarily caused by severe starvation, as well as purging behaviors.

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