Gut Microbiome and Obesity. How to Prove Causality?

In recent years, the gut microbiota (the microorganisms that live in our digestive tract) has become an area of great interest. Indeed, this intestinal microbial community performs essential functions in maintaining our health, and has been proven to influence host physiology and metabolism. Thereby, dysregulation of this gut microbiota may be implicated in the development of various diseases, including obesity. However, studies rarely assess causality, which requires the use of germ-free animals and microbiota transplant. Using these strategies, some gut microbiota were shown to confer obesity and associated metabolic disorders to mice, suggesting a causative link between gut bacteria and metabolic diseases.