New York Daily News - http://www.nydailynews.com Can a virus make you fat? By LIZ NEPORENT Sunday, November 2nd, 2003 Jim Thornton, a 51-year-old health columnist for the magazine Field & Stream, is an identical twin. Although he and his brother, John, have always exercised about the same amount and have similar eating patterns, Jim is 40 pounds heavier. "Neither of us is by any means overweight," he's quick to point out, "but I always wondered about that weight difference." Perhaps Thornton has something in common with chickens. In the 1970s, Dr. Nikhil Dhurandhar, an obesity researcher who holds the William Hardy Chair in obesity research at Wayne State University in Michigan, began studying a viral disease that was killing chickens by the thousands in India. He noticed that infected birds didn't waste away as they got sicker, but instead, packed on pounds — up to 50% more fat tissue than uninfected birds. Oddly, the sick chickens tested low for levels of cholesterol and triglycerides (fat in the bloodstream). "Normally, obesity in any species is associated with high levels of cholesterol and triglycerides," Dhurandhar says. Dhurandhar noticed something even stranger about the infected birds: They did not seem to eat more as they gained weight. Eventually Dhurandhar and his research team identified the cause of the birds' sickness as adenovirus-36, or Ad-36, a highly infectious microbe that affects animals as well as people. It was first isolated in humans in 1978 in the fecal matter of a 7-year-old diabetic girl. Based upon the discovery of Ad-36, Dhurandhar began to theorize that it might be a contributing factor to the skyrocketing obesity epidemic in humans. To test his theories, Dhurandhar performed a series of studies while at the University of Wisconsin at Madison, where he looked at the blood samples of numerous subjects for the existence of Ad-36 antibodies. An antibody is a chemical produced by the body to fight a particular condition; its presence is a sort of biological thumbprint that proves a person was infected by the virus that causes the condition at some point. More than 30% of the obese subjects tested positive for Ad-36 antibodies compared to only 5% of normal-weight individuals. When the researchers factored out 29 other possible sources of weight gain, such as genetics, family history and lifestyle, subjects did not differ in any other respects. The Ad-36-positive subjects were among the most obese in the study, but paradoxically had low cholesterol and triglyceride levels - just like the chickens in India. Another group of investigations done in Germany looked at nearly 100 pairs of identical twins. Researchers found that when one twin tested positive for Ad-36 antibodies, he always weighed more and had a higher percentage of body fat than the uninfected twin. In fact, several years ago Thornton sent blood samples from both him and his twin brother to Dhurandhar when he was researching an article on obesity-causing viruses. Thornton tested positive for the Ad-36 antibody, while his svelte-by-comparison twin did not. "It freaked me out to think that there's a possibility that a microbe could be messing with my metabolism," he says. He does observe, however, that his cholesterol levels are fairly high and that at 6-foot-1, 175 pounds, he's far from obese. How might one catch a case of heftiness from Ad-36? Dhurandhar says that the most likely transmission method is airborne. "In animal experiments, when infected animals were kept in the same room with noninfected animals, the noninfected animals became infected in a matter of days, even though there was no direct contact," he says. Dhurandhar strongly warns that more work, particularly by virologists, needs to be done. "You certainly cannot reliably translate the results of animal experiments to humans," he says. However, the notion that obesity could, in some cases, be caught like a common cold is not so farfetched. Researchers have blamed many chronic health conditions on infections. Ulcers, for example, were once thought to be caused by high stress and poor diet, but now the ulcer bug, Helicobacter pylori, is an accepted medical reality and ulcers are most commonly treated with antibiotics. Ongoing studies are focusing on microbial causes for everything from heart disease to depression. Looking at cause and effect Scientists speculate that Ad-36 amplifies fatness by increasing the number and size of adipocytes (fat cells) and by stimulating immature adipocytes to bloom more quickly. Animals infected with Ad-36 may wind up with three times more fat cells than uninfected animals, as well as vastly decreased metabolisms. "We also found that Ad-36-infected fat cells have reduced leptin levels," says Dhurandhar. Leptin is a recently discovered hormone that seems to regulate fat storage, metabolism and appetite. When you gain weight, leptin levels should rise, signaling the body to put the breaks on fat accumulation. Dhurandhar speculates that those who are Ad-36-positive may not be able to produce enough leptin to normalize fat metabolism. But not all scientists are convinced that you should edge away from that portly gentleman in the elevator when he sneezes. "We don't know whether the virus causes weight gain or shows up after you've already gained the weight," says Dr. Steven Heymsfield, Departmental Director of the Obesity Research Center at St. Luke's Roosevelt Hospital. In other words, Ad-36 could be a marker that shows up after fat cells multiply, rather than the cause of the excess adipose itself. Still, Heymsfield admits that the research is compelling and he'd like to see if further investigation will establish a cause-and-effect relationship. If Ad-36 is shown to cause excessive weight gain in humans, even when they don't overeat, it's not clear how contagious it may be, especially once the carrier has already reached full corpulence. It's also unclear how many other viruses may have similar effects. And certainly scientists are not suggesting that all obesity is communicable, though many experts don't think the worldwide spread of obesity can be totally explained by supersized portions and a couch-potato lifestyle. Viruses and other infectious entities may well be a contributing factor. The Wayne State University research team, led by Dhurandhar, recently received a National Institutes of Health grant to further study the concept of "infectobesity." __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free web site building tool. 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