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Infectious Viruses Linked to Obesity

Breaking News - February 2006 - Week 1

(Feb 1, 2006)

Healthcare in  the News

-- It is bad enough that so many people have to work so hard to lose or maintain weight. But now, some researchers think that obesity might actually be infectious.

Picture of scale and tape measure

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

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

"Obesity is a complex, chronic disease," notes lead researcher Leah D. Whigham, Ph.D., a research scientist in the department of nutritional sciences at the University of Wisconsin, Madison.

"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," Dr. Whigham states.

Animal Evidence Linked to Humans

The theory that viruses could play a part in obesity began several decades ago when researchers noticed that chickens in India infected with the avian adenovirus SMAM-1 had significantly more fat than non-infected chickens.

The discovery was intriguing because the explosion of human obesity, even in poor countries, has led to suspicions that overeating and lack of exercise were not the only culprits in the rapidly widening human girth. Since then, Ad-36 (a strain of adenovirus specific to humans) has been found to be more prevalent in obese humans.

However, the mechanism linking the virus to obesity is unclear.

Dr. Whigham's 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 in humans is not entirely new: earlier evidence suggests that two other adenoviruses, Ad-36 and Ad-5, are also virus strains that 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 [latest] 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 [Ad-5, Ad-36, and Ad-37], also are linked to obesity, Dr. Whigham says.

To this end, the researchers also developed a method of testing the effect of these adenoviruses in human fat cells.

Dr. Whigham says the commonviruses "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 adds.

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

Other Experts Question Findings

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

"There are far more satisfying explanations for epidemic obesity," says 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 says.

Dr. Katz says there is 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 says.

"Any contribution that adenoviruses make to epidemic obesity is certain to be little more than specks of dust compared with these 'obesigenic' factors," Dr. Katz continues.

Another expert agreed with Dr. 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," says Lona Sandon, R.D., 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," Sandon notes.

But for now, Sandon says, 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," states Sandon.

More Study Needed, Researchers Agree

Researchers now must identify all ofthe viruses that possibly cause human obesity, devise a screening test to identify people who are infected, and develop a vaccine.

However, screening tests and vaccines are still a long way off.

In the future, Dr. 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 says. "We are still a long way from that, because first we have to know how many of the human adenoviruses cause obesity."

The findings do not mean eating right and exercising are a waste of time, Dr. Whigham says.

"It is important for people to pay attention to those factors," she says. "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."

Always consult your physician for more information.

For more information on health and wellness, please visit health information modules on this Web site.

What Causes Obesity?

In many ways, obesity is a puzzling disease. How the body regulates weight and body fat is not well understood.

On one hand, the cause appears to be simple in that if a person consumes more calories than he or she expends as energy, then he or she will gain weight.

However, the risk factors that determine obesity can be a complex combination of genetics, socioeconomic factors, metabolic factors, and lifestyle choices, as well as other factors.

Some endocrine disorders, diseases, and medications may also exert a powerful influence on an individual's weight.

Factors which may influence the occurrence of obesity include, but are not limited to, the following:

Studies have shown that a predisposition toward obesity can be inherited. The chance of being overweight increases by 25 percent if one or both parents are obese. Where a person carries weight - the hips or around the middle - is also strongly influenced by heredity.

metabolic factors
How a particular person expends energy is different from how someone else's body uses energy.

Both metabolic and hormonal factors are not the same for everyone, but these factors play a role in determining weight gain. Recent studies show that levels of ghrelin, a peptide hormone known to regulate appetite, and other peptides in the stomach, play a role in triggering hunger and producing a feeling of fullness (satiety).

socioeconomic factors
There is a strong relationship between economic status and obesity, especially among women. Women who are poor and of lower social status are six times more likely to be obese than women of higher socioeconomic status.

The occurrence of obesity is also highest among minority groups, especially among women. Seventy seven percent of African-American women 20 years old or older are overweight.

lifestyle choices
Overeating, along with a sedentary lifestyle, contributes to obesity. These are lifestyle choices that can be affected by behavior change.

Eating a diet in which a high percentage of calories come from sugary, high-fat, refined foods promotes weight gain. And, as more US families eat on the go, high-calorie foods and beverages are often selected.

Lack of regular exercise contributes to obesity in adults and makes it difficult to maintain weight loss. In children, inactivity, such as watching television or sitting at a computer, contributes to obesity.

Obesity has a far-ranging negative effect on health. Each year obesity-related conditions cost over 100 billion dollars and cause an estimated 300,000 premature deaths in the US.

Always consult your physician for a diagnosis.

Online Resources

(Our Organization is not responsible for the content of Internet sites.)

American College of Cardiology

American Diabetes Association - Weight Loss Matters

American Journal of Physiology - Regulatory, Integrative and Comparative Physiology

American Society of Bariatric Physicians

Centers for Disease Control and Prevention (CDC)

Everyday Choices

National Heart, Lung, and Blood Institute (NHLBI)

National Institutes of Health (NIH)

NIH on Obesity

Office of the Surgeon General of the United States - Overweight and Obesity

US Department of Health and Human Services (HHS)

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