Reviewing Evidence from Clinical Trials for the Role of the Gut Microbiome in Disease
Many lines of evidence strongly suggest that alterations to the gut microbiome are an important contributing factor in the onset and progression of many different conditions, including age-related conditions. Comparatively few clinical trials touch on this relationship, however, despite the recent approval of a fecal microbiota transplant intervention for the treatment of Clostridioides difficile infection. That will change with time, but for now there is sufficiently little clinical trial data that a short paper can summarize it all.
Composed of an elaborate ecosystem of bacteria, fungi, viruses, and protozoa residing in the human digestive tract, the gut microbiome influences metabolism, immune modulation, bile acid homeostasis, and host defence. Through observational and preclinical data, the gut microbiome has been implicated in the pathogenesis of a spectrum of chronic diseases ranging from psychiatric to gastrointestinal in nature. Until recently, the lack of unequivocal evidence supporting a causal link between gut microbiome and human health outcomes incited controversy regarding its significance. However, recent randomised controlled trial (RCT) evidence in conditions, such as Clostridioides difficile infection, cancer immunotherapy, and ulcerative colitis, has supported a causal relationship and has underscored the potential of the microbiome as a therapeutic target.
This review delineates the RCT evidence substantiating the potential for a causal relationship between the gut microbiome and human health outcomes, the seminal observational evidence that preceded these RCTs and the remaining knowledge gaps. The association between the gut microbiome and human health has long been supported by multiple lines of observational evidence including in vitro, in vivo, and epidemiologic data. Recent RCTs of microbiome therapeutics have bridged the gap between association and causation and have definitively demonstrated that microbiome-altering therapeutics can improve human health outcomes in CDI. Further, smaller RCTs in UC and cancer immunotherapy, but not obesity, suggest the probable benefit of microbiome therapeutics across other indications as well.