Obesity could be - quite literally - contagious, say Yale scientists, who have discovered that it can be triggered by changes in microbes in the stomach.
Along with chronic liver disease, they say, obesity can be caused by a family of proteins that alter populations of intestinal microbes.
"When healthy mice were co-housed with mice that had altered gut microbes, the healthy mice also developed a susceptibility for development of liver disease and obesity," says Richard A. Flavell, professor of immunobiology at Yale School of Medicine.
The proteins in question, inflammasomes, are responsible for launching the immune system’s inflammatory response, and act as sensors and regulators of the microbial environment of the intestines.
And the Yale team found that a deficiency in components of two particular inflammasomes in mice led to an increase in bacteria which determined the severity of non-alcoholic fatty liver disease (NAFLD) and obesity in the mice.
NAFLD is the result of metabolic syndrome, a collection of disorders that includes obesity and diabetes, and is the leading cause of chronic liver disease in the western world.
Up to 30 million people are believed to suffer from NAFLD in the US alone. Twenty percent of sufferers develop chronic liver inflammation, placing them at risk for cirrhosis and liver cancer - and, until now, nobody has known why.
The next step, says Flavell, is to extend this research to humans and to identify more precisely the bacteria involved in the progression to liver disease.
"We found, in mice, that targeted antibiotic treatment brought the microbial composition back to normal, and thus eased the liver disease," he says.
"Our hope is that our findings may eventually lead to a treatment for humans."