Gut dysbiosis in anorexia nervosa patients

Anorexia nervosa (AN) is a devastating eating disorder in which a patient severely restricts food intake and may have purging behaviors. AN of course results in physical harm but there are also very significant psychosocial effects because of the disease. Studies have shown that the gut microbiome plays an important role in weight gain and it is therefore reasonable to believe that gut dysbiosis could be seen in individuals with anorexia nervosa.

Scientists in Japan characterized the microbiome of AN patients and compared them to healthy controls. They studied 25 women with AN and compared their microbiomes to 21 age-matched healthy females. They found that AN patients had a lower amount of total bacteria and specifically, lower amounts of C. coccoides group, C. leptum subgroup, B. fragilis, and Streptococcus.  

Several papers have shown the importance of gut bacteria on weight gain including those showing the impact that antibiotic use in poultry has on creating larger chickens. Other studies include those linking obesity to specific gut bacteria as well as studies that show transplantation of bacteria, specifically Christensenella minuta, reduced weight gain in mice.

These studies comprehensively show that there is some connection between gut bacteria and weight gain and therefore investigating it as a therapeutic mode for anorexia nervosa is logical. While this study was small in scale and no causal links can be made, it is important to understand that gut bacteria differs between AN patients and healthy controls. Microbiome therapies may be an option for treating anorexia nervosa.

The anorexia nervosa gut microbiome differs from healthy controls and is related to mental health

Two photographs, before and after treatment for anorexia

Anorexia nervosa is devastating condition in which an individual purposely starves themselves leading to severely low weight.  In addition, most patients with anorexia have depression, and there is a definitely mental aspect to this disease.  The disease then, has both dietary and mental components, making it extremely interesting to microbiome scientists, because the microbiome is implicated with both of these facets.  Scientists from UNC recently conducted a preliminary study on both of these aspects of the disease by comparing the microbiomes and mental state of anorexic patients before and after treatment, along with healthy controls.  They published there results last week in the journal Psychosomatic Medicine.

Sixteen patients with anorexia nervosa who sought treatment for their disease had stool samples collected at admission to the hospital as well as their mental health assessed.  Ten of these individuals that made partial recoveries (improved body mass index) were discharged from the hospital and donated stool samples and had their mental health assessed upon leaving.  The researchers discovered that the patients’ microbiomes severely lacked diversity compared to aged matched controls, and that was true for both admission and discharge from the hospital.  The scientists noted though, that the patients that left the hospital had microbiomes that more resembled the control individuals than when they entered.  For example, the anorexic patients had very little Clostridia when they entered the hospital, but these populations rebounded during treatment.  In terms of the mental health aspect of anorexia and the microbiome, the researchers found a direct association between eating disorder psychopathology and microbiome diversity, with lower diversity corresponding to worse eating disorder psychopathology.  The same was true for depression, as the degree of depression was inversely correlated with bacterial diversity.  In terms of individual families of bacteria, a lack of Ruminococcaceae had the strongest association negative mental state.

This study shows that a lack of eating decreases gut flora diversity and negatively impacts the microbiome.  While not surprising, this lack of diversity will almost certainly cause a dysbiosis that detriments many other aspects of health.  One of these, in the case of anorexia, may be mental health, but of course it is not clear which causes which, or if there is any causation or merely just correlation.  In any event, disorders that have both mental and dietary components are extremely fascinating to investigate, as it is possible the microbiome is of primary importance to these diseases.

Research is needed on the role of the microbiome and anorexia nervosa

Sketches of Miss A before (top) and after (bottom) treatment for anorexia nervosa by William Withey Gull.  Dr. Gull was among the first people to be clinically establish and treat anorexia, and was responsible for naming the disease.

Yesterday we discussed the latest research on the microbiome and obesity.  Today we wanted to share some thoughts on the other end of the spectrum: the microbiome and anorexia nervosa.  This week in the International Journal for Eating Disorders there was a call for research by doctors from the University of North Carolina to investigate the microbiome’s role in this disease.

Anorexia nervosa is a neurological disease characterized by self-starvation.  It often occurs with depression and other affective disorders.  It has severe side effects such as heart disease and seizures, which makes it the deadliest neurological disease, with around 5% of cases becoming fatal.  The causes of anorexia are complex, but genetic, social, and environmental risk factors all exist. 

Anorexia nervosa is a disease that is very likely implicated with the microbiome, perhaps profoundly.  It coincides with our understanding of the so-called gut-brain axis, which has already been linked to depression, anxiety, and appetite, which are distinctly awry in anorexia sufferers.  The relationship between anorexia and the microbiome is largely unknown.  Studies have indicated those suffering from anorexia have very unique microbiomes with similar bacterial that are not commonly found in the gut, but these studies are hardly convincing and not robust. 

Treatment for anorexia always includes dietary interventions, but these are not always effective in reestablishing normal weight, and relapse occurs in around half of all patients.  Recovery and therapeutics should also consider the microbiome.  Research on malnourishment in Africa has produced a wealth of literature on the importance of a balanced, robust, and healthy microbiome to nutrition and weight.  Simply adding calories to a diet is often not enough to improve health in the malnourished because their dysbioses, and the same phenomenon may also occur in patients suffering from anorexia nervosa.

Because the microbiome may be fundamental to both the neurological and dietary aspects of the disease, the authors of the paper encourage further research.  They suggest that microbiome transplants may be important to both physical and mental healing.  Anorexia nervosa is a complex disease, but research on the microbiome is crucial to fully understanding it.