Is obesity contagious?

Research showed that Adenovirus-36 (Ad-36), a common cause of respiratory and eye infections, caused animals to pack on the pounds in lab experiments. Obese people were three times more likely to have been infected with Ad-36 than thin people in a large study of humans. Now researchers have shown that exposure to the virus caused adult human stem cells to turn into fat-storing cells.
Dr. Magdalena Pasarica, who led the study, obtained adult stem cells from fat tissue of people who had undergone liposuction. Half of the stem cells were exposed to the virus Ad-36.  After a week, most of the infected stem cells developed into fat cells, while the uninfected cells were unchanged.
The researchers note that Ad-36 is just one of 10 pathogens linked to obesity and that more may be out there. They note that some people might find it hard to believe that a virus could be responsible for obesity. "Certainly overeating has something to do with gaining weight. No doubt about that. But that is not the whole truth. There are multiple causes of obesity. They range from simple overeating to genes to metabolism and perhaps viruses and infections."

Obesity can be "contagious" in a variety of ways:

• Studies have linked an imbalance in the ratio of microorganisms in your gut, the home of the immune and digestive system, to obesity. Specifically a higher ratio of organisms that contribute to inflammation and improper assimilation can cause someone to hold onto weight.
• Various studies have shown that viruses in and of themselves are linked to obesity.
• Sociology is finding that if you are friends with someone who is overweight or have family members who are, you are at higher risk of becoming overweight as well.

According to Harvard researchers, you're more likely to become obese if you're in contact with obese people. The scientists said that your chances of becoming obese increase by 0.5% with each obese family member, friend, or coworker you have in your social network.