There have been theories circulating for some time now that obesity is not just a genetic or physiological disease, but is actually an infectious one, which means that it is a result of contact with an infectious agent. There might just be proof in that, as published in the January issue of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology. Apparently, diet , genetics, and a sedentary lifestyle cannot fully account for the prevalence of obesity "epidemic", which in the last 30 years has doubled in adults and tripled in children in the US alone.

In this study, researchers have found that the human adenovirus Ad-37 causes obesity in chickens, and two other related viruses, Ad-36 (which is associated with human obesity) and Ad-5, also cause obesity in other animals.

The authors admit that there is still much to learn about how these viruses work.

"There are people and animals that get infected and don't get fat. We don't know why. Among the possibilities: the virus hasn't been in the body long enough to produce the additional fat; or the virus creates a tendency to obesity that must be triggered by overeating."

Succeeding research will have to be performed to:

• identify the viruses that cause human obesity
• devise a screening test to identify people who are infected
• develop a vaccine.

Read full report from the American Physiological Society Press.