New research suggests that biggie-size portions and our sedentary lifestyle aren’t the only reason why some of us are piling on the pounds. Scientists at Emory University reveal that a universe of bacteria — the so-called gut microbiota — that live in human stomachs can pile on the pounds in mice when they lack a protein known as toll-like receptor 5 (TLR5).

Without TLR5, gut bacteria can overflourish, triggering an inflammatory state as the body fights back.