It is reported that when human stem cells are exposed to a common virus they turn into fat cells. The cells didn't just change, but they stored fat too. It proves that some cases of obesity could be caused more than just a big appetite and not enough physical activity.
For several years, researchers looked for a link between obesity and the adenovirus-36. They found that a higher percentage of fat people were infected with the virus than non fat people. When they exposed animals to the virus, the animals fattened up. The found a gene in the virus that caused animal to get obese. The also took fat tissue from people who had liposuction and removed adult stem cells from the tissue and exposed the cells to the virus in the lab. More than half of the stem cells turned into fat cells.
If there is a vial cause to obesity, a vaccine could be created within the next 5 to 10 years to prevent the virus from making some people fat.