Obesity and the gastrointestinal microbiota: a review of associations and mechanisms.

The two-way obesity model that considers only the interplay between humans and their environment has been revised to include the gastrointestinal microbiota. Notable perturbations in the bacterial communities in obese individuals have been uncovered. Research is helping to distinguish between the obesogenic mechanisms attributable to diet and those that may be associated with the microbiota. Examples include studies in which transplant of the microbiota from murine models of weight loss (gastric bypass) into germ-free mice resulted in significant weight loss. Several mechanisms have been identified that suggest the microbiota may play a role in obesity development and propagation. There is some evidence from animal and human studies that the microbiota in the obese harvests energy more effectively and may manipulate host gene function leading to increased adiposity, aggravation of inflammatory mechanisms, metabolic endotoxemia, and metabolic dysfunction. Research findings highlight the potential of the microbiota to influence body weight and they allude to its potential therapeutic use in tackling the costly global epidemic of obesity.