Gut microbiota dysbiosis has been reported as an environmental factor involved in anorexia nervosa (AN) development. A review published in 2015, led by Dr. Cynthia Bulik from Departments of Nutrition and Psychiatry from the University of North Carolina at Chapel Hill (North Carolina) and the Department of Medical Epidemiology and Biostatistics from the Karolinska Institutet (Stockholm, Sweden), has previously reported that there is a dysbiosis or microbial imbalance in the gut microbiota in patients with AN. Although it is not yet clear whether gut commensal microbes have a causative role in AN, this review also reported that gut microbial shifts in patients with AN correlated with anxiety and depression measures and also conferred anxiety and depression to germ-free mice.
When exploring a further step regarding the role of the gut microbiota in the maintenance of and recovery from AN after weight gain -which is the initial treatment for those with AN-, a recent study led by Dr. John Penders, from the Department of Medical Microbiology at Maastricht University Medical Centre (The Netherlands), has found that the gut microbiota of AN patients (55 patients before weight gain, of which 44 were available afterwards) is perturbed in comparison to normal weight participants (n = 55) and is accompanied by increased concentrations of branched chain fatty acids (consisting of isobutyrate and isovalerate). Besides this, gut dysbiosis does not recover after weight gain and/or normalisation of eating behaviour in addition to several gastrointestinal symptoms.
Another new study, led by Dr. Elisa Borghi from the Department of Health Sciences at the Università degli Studi di Milano in Milan (Italy), has found that gut dysbiosis, microbial metabolite profile, and psychopathological scores are closely related in those with AN (n = 15) when compared to age-, sex- and ethnicity-matched healthy controls (n = 15).
AN subjects showed a gut dysbiosis, with every taxonomic level affected. Specifically, there was a significant increase of Enterobacteriaceae and of the archeon Methanobrevibacter smithii when compared to healthy controls, whereas the genera Roseburia, Ruminococcus and Clostridium were depleted.
Faecal concentrations of total short-chain fatty acids (SCFAs), butyrate, and propionate were significantly reduced in AN samples. Regarding systemic microbial metabolites, no differences were detected in serum SCFAs between the two groups.
Correlation tests were carried out to find possible associations between gut microbiota composition, psychopathology tests, and clinical status. BMI showed a negative association with Bacteroides uniformis, with alanine aminotransferase (an enzyme involved in liver function), and with several psychopathological parameters (obsession-compulsion, anxiety, and depression), and a positive correlation with total leukocyte count. According to the authors, these data support the idea that the anthropometric parameter BMI has the best predictive value for both gut dybsiosis and metabolic alterations. Besides this, faecal butyrate concentrations inversely correlated with depression and anxiety scores, whereas propionate directly correlated with insulin levels and with the relative abundance of Roseburia inulinivorans, which is a propionate producer. Other biochemical parameters were not significantly associated with gut microbiota composition.
To sum up, patients with AN exhibit a gut dysbiosis and increased microbial metabolites that is associated with anthropometric, clinical, and psychological characteristics of those with AN. Further studies are needed in order to elucidate whether these associations have a causal role in the pathophysiology of AN.
Mack I, Cuntz U, Grämer C, et al. Weight gain in anorexia nervosa does not ameliorate the faecal microbiota, branched chain fatty acid profiles, and gastrointestinal complaints. Sci Rep. 2016; 6:26752. doi: 10.1038/srep26752.
Kleiman SC, Carroll IM, Tarantino LM, Bulik CM. Gut feelings: A role for the intestinal microbiota in anorexia nervosa? Int J Eat Disord. 2015; 48(5):449-51. doi: 10.1002/eat.22394.
Borgo F, Riva A, Benetti A, et al. Microbiota in anorexia nervosa: The triangle between bacterial species, metabolites and psychological tests. PLoS One. 2017; 12(6):e0179739. doi: 10.1371/journal.pone.0179739.