Gut microbiota induces weight gain and inflammation in the gut

Obesity and the metabolic syndrome are complex disorders resulting from multiple factors including genetics, diet, physical activity, inflammation, and gut microbes. Animal studies have identified roles for each of these, however surprisingly the contribution(s) specifically attributed to the gut microbiota remain unclear, as studies have used combinations of genetically altered mice, high fat diet, and/or colonization of germ free mice, which have an underdeveloped immune system. In this study, we show, for the first time, that human fecal gut microbes promote obesity and inflammation in mice with a fully developed immune system, independent of manipulations of genetics and diet. We find that the obese human microbiota alone is sufficient to cause weight gain and systemic and local inflammation in the gut and adipose tissue and contrary to studies of gut microbes using animals on obesogenic diets, these changes occur in absence of gut barrier leak.