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.

The effects of fasting and starvation on the microbiome

Researchers at St. Mary’s University, in Texas, published a study in FEMS Microbiology Ecology about the impact that fasting and starvation have on the gut microbiome. Organisms from five different vertebrate classes were studied and the changes in the composition of their colon and cecum microbiome were observed in response to different fasting periods.

Results differed among the animals studied in terms of diversity of their colon microbiome. Tilapia showed a continuous increase in diversity, southern toads showed a 33% increase in early-fasting and a 51% increase in late-fasting, leopard geckos showed no difference, Japanese quail showed less diversity in long-term fasting, and weanling mice showed a 15-22% increase in diversity. Results for the observed cecum microbiome phylogenetic diversity, compared to the respective nourished vertebrates, are as follows: Tilapia showed a decrease in diversity, quail showed a decrease at the early-fasting stage but a return to normalcy at later stages, mice showed no changes.

The only similarity in colon bacteria identified from this study was that the tetrapods (toads, geckos, quail, mice) all showed a decrease in abundance of Coprobacillus and Ruminococcus. In the cecum, tilapia, quail, and mice showed an increase in Oscillospira and a decrease in Prevotella and Lactobacillus. While it must be considered that these diverse hosts tend to house different microbial communities when healthy, which can account for the few similarities observed between the different vertebrates, the study results are important because they show that microbial responses to prolonged fasting varies between vertebrates.  

While these studies were conducted in non-humans, we know that starvation results in important changes in the microbiome.  People around the world suffer from starvation and malnutrition, and it is not only because they lack food and nutrients.  Instead they suffer from immature microbiomes, which can severely impact health.  Furthermore, diet interventions only temporarily repair the microbiome, so the effects of malnutrition persist after the intervention ceases.  Finally, the differences in microbiomes between developed nations and traditional societies may even play in a role in vaccine effectiveness, as we have previously discussed in our blog.