Gastric bypass surgery in mice alters the microbial makeup of their gut, and these changes may contribute to the rapid weight loss experienced after the surgery, according to a new study appearing in the 27 March issue of the journal Science Translational Medicine.

Researchers found that transplanting microbes harvested from mice that underwent surgery, into mice with no gut bacteria, led to weight loss (up to 5% of body weight) and decreased fat tissue in the mice who received the transplants.