Does a Fat Virus Really Exist?

There's evidence that a common virus may cause weight gain in some people. Here are the facts about this so-called fat virus.

The theory that a virus could play a part in weight gain began some time ago when Nikhil Dhurandhar, now an associate professor at the Pennington Biomedical Research Center in Louisiana, noticed that chickens in India infected with the avian adenovirus SMAM-1 had significantly more body fat than non-infected chickens. He found it strange that birds with a viral infection had so much body fat, and he wondered if the SMAM-1 virus could be causing the excess fat.

To find out, Dhurandhar infected a group of chickens with SMAM-1 and then compared them with a group of healthy chickens. All of the chickens ate similar amounts of food, but only the infected ones gained body fat. As a matter of fact, they became obese. He wondered if the virus could cause excess body fat in humans.

Any human infected by SMAM-1 would likely have antibodies in his or her blood, naturally created by the body to fight off the virus. Dhurandhar took blood samples from a group of obese people, and he found that 20% of them had antibodies to fight off SMAM-1. Dhurandhar now wondered if there could be a human adenovirus that could cause excess body fat.

There are 50 known human adenoviruses, and they cause everything from the common cold to gastrointestinal problems. Dhurandhar decided to study adenovirus-36 (AD-36). In several studies, chicken, mice and other animals infected with AD-36 became obese. In another study, blood samples from a group of people that included both lean and obese people showed that only 11% of the lean people but 30% of the obese people had antibodies to AD-36. It was determined that the virus causes excess body fat by causing more stem cells to convert to pre-fat cells and causing the pre-fat cells to become bigger fat cells.

Following Dhurandhar’s lead, other researchers have determined that at least two other human adenoviruses, AD-37 and AD-5, might also cause excess body fat.

With this evidence that at least one fat virus does exist, there are still several points that need to be considered.

In the one study, 11% of the LEAN people had antibodies to AD-36. How come they didn't get fat?
In the same study, 30% of the obese people had antibodies to AD-36, but 70% did not.
There is still much to learn about how human adenoviruses work.
Many scientists don't agree with the fat virus theory.

The bottom line is that certain viruses may contribute to excess body fat and obesity in some people, but the primary cause of being overweight or obese is consuming too many calories and not getting enough physical activity.