Mirko Trajkovski's team, at the University of Geneva (UNIGE), Switzerland, demonstrated few weeks ago that the absence of gut microbiota can be linked to increased brown fat activation as a mean of limiting obesity. Today, pursuing their research, the scientists show that mice exposed to cold experience a sharp shift in their microbiota composition, rendering them leaner and more sensitive to insulin. Transplantation of this cold-modified microbiota to germ-free mice is sufficient to enable complete tolerance to cold. Indeed, it increases their brown fat levels and thus improves their sensitivity to insulin, even without exposing them to cold. However, prolonged cold exposure can also attenuate the body weight loss as the body takes up more calories from the consumed food.