DATE: October 2, 2015
By: Susan C. Kleiman
In addition to my affiliation with UNC CEED as a PhD student under Dr. Cynthia Bulik, I have been fortunate to work with Dr. Ian Carroll in the UNC Center for Gastrointestinal Biology and Disease in launching our research examining the role of the intestinal microbiota in the emergence and maintenance of anorexia nervosa.
The Carroll lab is returning from the Gut Microbiome Conference 2015, which was held on September 26-27th in Huntington Beach and for which Dr. Carroll served on the organizing committee. It was a jam-packed two days of presentations covering everything from structure and function of the intestinal microbiota to how the latest research findings may influence clinical treatment of cancer, gastrointestinal disorders, and metabolic syndrome. Although eating disorders were not directly addressed in the presentations, there was still plenty to learn and bring back to the lab!
In his keynote address, Dr. Peter Turnbaugh (UCSF) invited us to think about our gut microbes as “synthetic chemists.” Did you know that at least 49 drugs are changed or metabolized by bacteria in our GI tract but that most of the genes responsible are completely unknown? Much of the research to date has focused on understanding the structure of our intestinal microbiota (i.e., which microbes are present), but we are starting to move to understanding the activity and function of these microorganisms, the metabolites they produce, and how these things influence both health and disease. The possibilities for new therapies, biomarkers, and drugs are infinite, and we are looking forward to implementing some of these new techniques with our eating disorders research.
Studying an individual’s intestinal microbiota usually involves isolating bacterial DNA from a stool sample, but Dr. Christopher Chang (UNM) introduced us to other approaches that could indirectly measure gut microbes and provide evidence of microbial dysbiosis (defined very elegantly by Dr. Janelle Arthur of UNC as the bloom or mislocalization of resident microbes). As more than 99 percent of our body’s hydrogen production is in the colon (around 13 liters per day!), hydrogen breath testing provides a way to measure bacterial fermentation and could help identify the presence of bacterial overgrowth, diminished GI motility, etc.
It’s tempting to think about the intestinal microbiota as being either “healthy” or “diseased,” but as was pointed out by Dr. Balfour Sartor (UNC), there is a delicate balance between injurious and protective bacteria that is unique to each individual. Because of this, individuals will also respond differently to the presence or absence of particular bacteria—meaning that, unfortunately, there will never be a single intervention for everybody. The ultimate goal of our research into the intestinal microbiota of patients with eating disorders is to develop new therapies that would correct microbial dysbiosis by selectively altering bacteria—either decreasing the number/function of injurious bacteria or increasing the number/function of protective bacteria. We have much to learn about the clinical applications of probiotics, prebiotics, synbiotics, and even fecal microbial transplant, so stay tuned!
Dr. Ruchi Mathur (Cedars-Sinai Medical Center) brought up a lingering question about microbial dysbiosis in anorexia nervosa that relates, not to bacteria, but to archaea (single-celled, prokaryotic organisms that are distinct from bacteria and often found in very extreme environments). Back in 2009, the first evidence emerged that patients with anorexia nervosa may have higher levels of Methanobrevibacter smithii (M. smithii), a methanogen (i.e., methane producer) associated with increased energy harvest from the diet. Results of a methane breath test correlate with M. smithii levels, and a positive breath test has been associated with higher initial weight/BMI and attenuated weight loss in obese individuals participating in a weight loss trial. Methane also slows intestinal transit, which can lead to constipation but also increases the amount of time that bacteria have to harvest energy from the food we’re digesting. Could higher methanogen levels in patients with anorexia nervosa be an adaptive response to a restrictive diet?
There is still lots to come on the intestinal microbiota in eating disorders, so check back on this blog for all the latest on our research!