A week ago, when I first heard the story about the so-called fat virus, I was suspicious. What medical commentator wouldn't be. Was this yet another science fiction story masquerading as science? So I contacted the principle researcher in the field, Dr. Nikhil V. Dhurandhar at the Pennington Biomedical Research Center in Baton Rouge, LA. Dhurandhar was kind enough to immediately email me his last several studies on the subject, published in the International Journal of Obesity, Diabetes, Archives of Virology, and elsewhere. The studies convinced me of several things:

* Dhurandhar's research, conducted over the past 6 years, is impressive but it is not entirely new - though the news media has suddenly attached to it.

* The previous research conducted in animals is substantial. The virus in question, a respiratory adenovirus known as AD-36, one of 50 adenoviruses to cause cold-like symptoms, has shown that mice, chickens, and monkeys all put on greater than two times more body fat than normal in the months following infection with this virus.

* The virus causes this effect by stimulating adipose (fat) cells in the body to replicate, and by improving the sensitivity of these cells to insulin, so more sugar is absorbed. Over time, resistance to the virus should occur as antibodies develop, but long-term studies haven't yet been done.

* It is unethical to inject this virus into humans, but Dhurandhar has checked humans for the presence of this virus and has found that almost a third of obese people have been exposed to it, three times the number of thin people who have antibodies to the virus. This associated finding doesn't prove that the virus leads to weight gain in humans, but it is suspicious.

* A vaccine may one day be developed against AD-36. In the meantime, the technology exists to check people at risk for obesity to see if they have the virus.

* The focus on this virus should NOT take needed attention away from the most common causes of obesity including sedentary lifestyle, poor diet, and low thyroid (found in 1/3 women). AD-36 may be a contributing factor in a minority of patients, but it is not an explanation or an excuse for the growing obesity epidemic.

Dr. Marc Siegel is an internist and associate professor of medicine at the NYU School of Medicine. He is a FOX News medical contributor and writes a health column for LA Times, where he examines TV and movies for medical accuracy. Dr. Siegel is the author of "False Alarm: The Truth about the Epidemic of Fear"and "Bird Flu: Everything You Need to Know About the Next Pandemic." Read more at www.doctorsiegel.com