Is obesity infectious? A new study suggests that obesity, epidemic worldwide, may be caught like a cold or flu. A research group found that altering microbes that live in the stomach, alterations that can be contagious, can trigger obesity and chronic liver disease in a study published Wednesday in the journal Nature.

Researchers fed a Western-style high-fat diet to mice bred for fatty liver disease and saw, predictably, that these mice gained weight. Flavell said microbes in the mice are to blame for the mice's obesity. The mice with the liver disease had a disturbed immune system, which caused a change in their gut bacteria.

However when healthy mice were placed in the cage with them, the researchers saw something unexpected. Mice with fatty liver disease passed on gut microbes to normal mice that then became obese and got liver disease.

We could make a mouse fatter just by putting it in the same cage as the other mouse. Richard Flavell one of the researchers and a professor of immunobiology at Yale School over medicine, told Yale News.When the researchers eliminated the gut microbes with antibiotics, both obesity and liver disease decreased. 

Flavell said bacteria may be as important as diet in dermining the cause of obesity. [Diet] is an essential part of the weight gain of the healthy as well as the immune compromised mice, he said. However, the bacteria make both kinds of mice fatter.  In others words, diet as well as the microbes contribute to the obesity.

Fatty liver disease is common in obese people, affecting 75 percent of the obese population. The mouse study shows that the environment may play a role in the disease development as well. This is a very thought-provoking study that underlines the role of the bugs that we all carry inside us in determining our susceptibility to liver disease and its complications, Jasmohan Bajaj, an associate professor of gastroenterology at Virginia Commonwealth University,  who was not involved in the study, told Live Science. He said these experiments form a key step forward.

While Flavell said that there is still a great deal of research to be done, he said that whether obesity is contagious in humans is something that should be very seriously looked at in people.

We found, in mice, that targeted antibiotic treatment brought the microbial composition back to normal, and thus eased the liver disease, Flavell told Yale News. Our hope is that our findings may eventually lead to a treatment for humans.