The Role of Human Gut Microbiota in Obesity

Traditionally, obesity has been conceptualized as an imbalance between energy consumed and energy expended. Thus the global rise in obesity has been ascribed to the rise in the ready availability of energy-dense foods coupled with physical inactivity. However, this is not the whole story. Evidence for a role of the gut microbiota in the development of obesity emerged from studies in germfree mice that are generally protected from obesity. A dramatic increase in body fat and insulin resistance occurs when gut microbes from obese animals are transferred to these lean mice. In human studies of the composition of gut microbiota, differences have been shown comparing lean and obese subjects. Changes are now well documented in response to weight loss and after bariatric surgery. Intestinal microbiota have been shown to provoke the low levels of inflammation observed in obesity through the absorption of bacterial lipopolysaccharide. There is also renewed interest in the gut virome, which is able to modulate the effects of the host microbiome. Evidence is beginning to emerge that modification of the intestinal microbiota may offer novel therapeutic options for the management of obesity and its associated metabolic conditions.