According to researchers in the U.S., a virus may be why some people are obese.
A study by scientists at the University of Wisconsin-Madison, has found that the human adenovirus Ad-37 causes obesity in chickens.
The finding supports evidence from other studies that two related viruses, Ad-36 and Ad-5, also cause obesity in animals.
According to Leah D. Whigham, the lead researcher in the new study, human adenoviruses may cause human obesity, but more research is needed before a screening test and vaccine become reality.
She says there is mounting evidence that certain viruses may cause obesity, in essence making obesity contagious, but the viruses that cause human obesity need to be identified before a screening test and vaccine can be developed.
The idea that viruses can cause obesity is contentious says Whigham despite evidence that factors other than poor diet or lack of exercise may be at work in the obesity epidemic.
The study notes that obesity has doubled in adults and has tripled in children in the United States in the last 30 years,and except for infectious diseases, no other chronic disease in history has spread so rapidly.
Whigham says people are more comfortable thinking that obesity stems from lack of control, and a big mental leap is needed to believe obesity is contagious.
As Whigham points out, other diseases once thought to be the product of environmental factors are now known to stem from infectious agents, such as ulcers, once thought to be the result of stress, the bacteria, H. pylori has now been found to be implicated.
The study says the simultaneous increase in the prevalence of obesity in most countries of the world is difficult to explain by changes in food intake and exercise alone, and suggests that adenoviruses could have contributed.
The Ad-37 virus has been implicated in animal obesity.
The theory is not new as a few decades ago scientists noticed that chickens in India infected with the avian adenovirus SMAM-1 had significantly more fat than non-infected chickens.
The discovery was intriguing then and the explosion of human obesity, even in poor countries, has led to suspicions that overeating and lack of exercise weren't the only culprits.
Since then, Ad-36 has been found to be more prevalent in obese humans.
In Whigham's study the researchers wanted to find out which adenoviruses (in addition to Ad-36 and Ad-5) might be associated with obesity in chickens.
The chickens were separated into four groups and exposed to either Ad-2, Ad-31, or Ad-37.
There was also a control group that was not exposed to any of the viruses.
The researchers measured food intake and tracked weight over three weeks before ending the experiment and measuring the chickens' visceral fat, total body fat, serum lipids, and viral antibodies.
Chickens inoculated with Ad-37 had much more visceral fat and body fat compared with the chickens infected with Ad-2, Ad-31 or the control group, even though they didn't eat any more.
The Ad-37 group was also generally heavier compared to the other three groups, but the difference wasn't great enough to be significant by scientific standards.
The authors concluded that although Ad-37 increased obesity in chickens, not all adenoviruses have this effect.
Whigham says there is still a lot to learn about how these viruses work, as there are people and animals that get infected and don't get fat and as yet it is not known why.
She suggests it is possible the virus has not been in the body long enough to produce the additional fat, or else the virus creates a tendency to obesity that must be triggered by overeating.
In view of the finding,' wash your hands' as well as exercise and eat healthy, might be sound advice in future.
The study is published in the January issue of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology published by the American Physiological Society.