washington scientists have recently found that obesity can spread between friends if they copy each others eating habits now a new study has suggested it could actually be infectious in the study published in the journal nature mice were engineered to have a immune deficiency leading to fatty liver disease and got fatter when fed a westernstyle diet but strikingly when these immunedeficient mice were put in the same cage as healthy mice the healthy mice started to come down with symptoms of liver disease and also got fatter researchers found the culprit microbes in the stomachs of the mice said richard flavell a professor of immunobiology because the mice had their immune systems disturbed the bacteria in their guts got out of wack he said we live in symbiosis with the gut bacteria but in the study the number of bad diseaseassociated bacteria increased 1000fold in mice with immune problems