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."
