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"To date, my lab and others have identified 11 to 12 microbes that cause obesity in animals," says Dhurandhar, who also happens to be president of The Obesity Society, an organization that advocates for research and programs to treat this complex condition. In studies, infected animals will gain 2.5 times as much weight as uninfected animals—even though they're eating the exact same amount of food. "We see these results in 60 to 100% of infected animals," he says. "It's a very high probability that if an animal is infected, it will become obese. Of course, we cannot conduct controlled experiments in humans like we can in animals." In other words, he can't infect humans to see if they become obese.
"But we can show associations between the virus and obesity," Dhurandhar says. Labs have found that people who are naturally exposed to adenovirus 36—one of a family of very common viruses—are 300 times more likely to be obese than people who haven't been exposed. Worldwide, more than 15,000 people in nine different countries have been tested for antibodies to the virus (usually the body fights off the virus, but the damage is already done), and with remarkable consistency, people who are obese are far more likely to show signs of infection.
"The virus infects stem cells that reside in fat tissue," Dhurandar explains. "It boosts their numbers, makes them differentiate into fat cells, and prompts them to store more fat—a vicious cycle that's hard to stop or reverse once it's begun." His hope is to stop it with a vaccine. Catching it early is especially important since a recent study published in the journal Pediatrics found that signs of infection were prevalent in obese children—but not in normal weight children.
"Think of it," says Dhurandhar. "We could get rid of obesity of infectious origin just like we did small pox." In fact, researchers in Korea are making progress on a vaccine: They've been able to successfully protect infected mice from becoming obese. They've also made strides in treatment of infected mice: Using a mulberry extract, an anti-inflammatory agent, they've been able to minimize weight gain. (Earlier studies showed that adenovirus 36 requires inflammation for obesity to take hold.)
A vaccine won't cure all obesity, says Dhurandar, but it could eliminate infectobesity—and about a third of obese people test positive for infection. He believes that, like cancer, obesity has several different root causes, and poor diet and a sedentary lifestyle still play a big role. "If someone says, 'I have cancer,' the first thing one asks is, 'What kind of cancer?' " he says. "That's why I like to use the term 'obesities.' It's not, to my mind, just one disease. There are different types with different origins." And infectobesity just might be preventable.
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