The reason behind obesity is not just limited to poor eating habits and a less active lifestyle, for viruses may also play a role in making people obese, an expert has suggested.
In an article published in the October issue of Mayo Clinic Proceedings, researcher Richard Atkinson, MD, director of Obetech Obesity Research Center in Richmond, reports that there is mounting evidence pointing to viruses as one reason in the worldwide obesity epidemic.
"The cause of obesity is not a secret -- if you consume more calories than you burn in daily activity, you gain weight. What is interesting is that much of the obesity epidemic cannot be explained just by Americans eating more and exercising less. There are other factors at play, and viruses causing obesity may be one of them," D Atkinson said.
He cited an experiment where researchers infected lab animals with a virus called Human Ad-36. The researchers recorded an increase in body fat and in the fat around organs within the abdomen. This virus could also be passed to other animals, which also gained weight.
Dr Atkinson reports also that he's previously found evidence of this same virus in humans. In a study of 502 people from three US cities, evidence of the virus was found in 30 percent of people who were obese and 11 percent of people who were lean.
He also highlighted a study that looked at 89 sets of American adult twins and screened them for Ad-36. Because twins tend to be similar in many characteristics, including body weight, the researchers looked at twin pairs where one twin tested positively for Ad-36 and the other did not.
"Antibody-positive twins were slightly, but significantly, heavier and fatter than their antibody negative co-twins. The infected twins had a higher BMI and a greater percent of body fat than the uninfected co-twins," he said.
In the mid-1970s, a virus called SMAM-1 was believed responsible for an increased death rate among commercially raised chickens in India. SMAM-1 is associated with decreased immune function and an increased accumulation of body fat in infected chickens.
Dr Atkinson reports that one study tested 52 obese humans for antibodies to SMAM-1. About 20 percent had SMAM-1 antibodies, indicating exposure to this virus. The study participants who had these antibodies were heavier and had a higher body mass index compared with the antibody-negative group.
His article also explores what current research has to say about the possible mechanisms underlying virus-induced obesity. Some research suggests that viral infections have a direct effect on adipocytes, cells that manufacture and store fat, turning on the enzymes of fat accumulation and recruitment of new adipocytes.
"The body of evidence linking adenoviruses to obesity in humans is now sufficient to think about the next step. Ideally, we could prevent infection and virus-induced obesity with a vaccine for the obesity viruses. Development of a human vaccine will take several years," he said.