Recent studies have shown we tend to eat more when the people around us do. But new research with mice takes that one further, revealing obesity may actually be contagious.

In the study, published online Feb. 1 in the journal Nature, mice engineered to have a particular immune deficiency predictably developed fatty liver disease and got heavier when fed a Western-style diet. But when those mice were put in the same cage as healthy mice, the healthy mice got fatter too, and even started to come down with symptoms of liver disease.

Researcher Richard Flavell, a professor of immunobiology at Yale School of Medicine, said stomach microbes could be to blame. When the mice’s immune systems were disturbed, their gut bacteria was also thrown for a loop — in fact, Flavell said the study showed the number of “bad,” disease-associated bacteria increased 1,000-fold in mice with immune problems.

He told LiveScience it was these bad bacteria that made their way from mouse to mouse, leading the healthy mice to experience changes in their microbes — which in turn made them fat.

But does the same thing happen in people?

Flavell said more research is needed to find out, especially because one way the mice transmitted bacteria back and forth was by eating each others feces — something humans don’t tend to do.

But since fatty liver disease is very common among the obese, affecting 75 percent to 100 percent of that population, Flavell said if further studies show his findings apply to people, it may suggest that approaches to obesity and fatty liver disease should address gut microorganisms, perhaps using antibiotics or probiotics in addition to traditional treatments.