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Obesity Might Be Catching

Infectious viruses may make fat cells fatter, researchers claim

MONDAY, Jan. 30, 2006 (HealthDay News) -- As if the close proximity of delicious, fattening foods weren't bad enough, obesity might actually be infectious.

That's the incredulous finding from new research involving overweight chickens; the study suggests that a contagious virus can make fat cells fatter.

"Obesity is a complex, chronic disease," noted lead researcher Leah D. Whigham, a research scientist in the department of nutritional sciences at the University of Wisconsin. "There are lots of factors contributing to the broad epidemic, but because of the rate of increase, it is very possible that it is partially due to an infectious disease."

The findings appear in the January issue of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology.

The research team found that the human adenovirus Ad-37 triggers obesity in chickens. Adenoviruses are a frequent cause of colds, and a number of other types of illnesses.

The finding is not entirely new: earlier evidence suggests that two other adenoviruses, Ad-36 and Ad-5, also cause obesity in animals. In addition, Ad-36 has been associated with human obesity.

"There is an additional human adenovirus that causes obesity in the animal model we used," Whigham said. "In this study, we showed that Ad-37 causes obesity in chickens."

There are more than 50 adenoviruses that need to be studied to see if others, beyond the three identified, also are linked to obesity, Whigham said. To this end, the researchers also developed a method of testing the effect of these adenoviruses in human fat cells.

Whigham said the common bugs "increase the fat in the fat cells. But we will still need to do animal studies to confirm those results." Still, the evidence is very strong that adenoviruses also cause obesity in humans, she added.

"There is quite a bit of already published data with Ad-36 and its association with obesity," she said. "If you look at obese people, more of them have antibodies to Ad-36 than lean people."

In the future, Whigham thinks that it may be possible to develop a vaccine against obesity to target these viruses. "A great way to handle the [obesity] epidemic is to come up with a vaccine," she said. "We are still a long way from that, because first we have to know how many of the human adenoviruses cause obesity."

The findings don't mean eating right and exercising are a waste of time, Whigham said.

"It is important for people to pay attention to those factors," she said. "We don't know how diet and exercise interact with the virus. Even if you are antibody positive, if you watch your diet and exercise, maybe it won't have the same effect. There are people who have the antibodies but are not obese."

One expert disagreed with the notion that viruses are key to the obesity epidemic.

"There are far more satisfying explanations for epidemic obesity, said Dr. David L. Katz, director of the Prevention Research Center Yale University School of Medicine and author of The Flavor Point Diet."We have more calories available per capita per day than ever before in history. And more and more of those calories are packaged in highly processed, flavor-enhanced, processed foods," he said.

Katz said there's a simpler explanation for why more Americans are getting fatter: because they can.

"We live in a profoundly 'obesigenic' world, one that makes weight gain the path of least resistance," he said. "Any contribution that adenoviruses make to epidemic obesity is certain to be little more than specks of dust compared with these 'obesigenic' factors."

Another expert agreed with Katz that viruses probably have only a small role to play in obesity.

"The obesity epidemic in the U.S. can be largely explained by our inactive, over-indulgent lifestyle behaviors," said Lona Sandon, an assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center, in Dallas. "It is possible that viruses may play a role in setting us up for becoming overweight, similar to how our genes may be programmed to lead to obesity under the right circumstances."

But for now, Sandon said, people need to stick with what works for preventing and treating obesity. "That's eating less and moving more. We may not be able to change our genes and environment, but we can change the way we eat and exercise."

More information

Learn much more about obesity at the U.S. National Institute of Diabetes and Digestive and Kidney Diseases.

SOURCES: Leah D. Whigham, Ph.D., research scientist, Department of Nutritional Sciences, University of Wisconsin, Madison; David L. Katz, M.D., M.P.H., associate professor, public health, director, Prevention Research Center Yale University School of Medicine, New Haven, Conn., and author, The Flavor Point Diet; Lona Sandon, R.D., assistant professor, clinical nutrition, Texas Southwestern Medical Center, Dallas, and spokeswoman, American Dietetic Association; January 2006 American Journal of Physiology-Regulatory, Integrative and Comparative Physiology
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