Obesity can be "caught" as easily as a common cold from other people's coughs, sneezes and dirty hands, scientists said Monday.
The condition has been linked to a highly-infectious virus which causes sniffles and sore throats.
Nikhil Dhurandhar, an associate professor at The Pennington Biomedical Research Center, in Baton Rouge, La., said the virus, known as AD-36, infects the lungs then whisks around the body, forcing fat cells to multiply and also causing sore throats.
"When this virus goes to fat tissue it replicates, making more copies of itself and in the process increases the number of new fat cells, which may explain why the fat tissue expands and why people get fat when they are infected with this virus," Dhurandhar said.
In one test, a third of obese people had the rare and highly contagious virus compared to just 11 percent of thinner people. Weight gain can last three months until the body has built up resistance to the bug.
New research supports earlier theories from studies on weight gain; evidence in tests on mice and chickens shows the bug could cause overweight people to gain weight.
"People could be fat for reasons other than viral infections, so it’s pointless for fat people to try to avoid infection," said Dhurandhar.
The study also reveals research claiming dieters always feel hungry because humans have a "natural body weight" and they will always suffer hunger pangs.
The Pennington Biomedical Research Center, a campus of the Louisiana State University system, conducts both clinical and basic research. Its mission is to promote healthier lives through research and education in nutrition and preventive medicine.