WHAT IS THE STORY?
A common cold virus could be responsible for obesity, according to recent media reports.

A US study found that Adenovirus-36 (Ad-36), which causes respiratory tract infections and conjunctivitis, left sufferers with larger and higher numbers of fat cells than those who were not infected.

The study claims to be the first to provide evidence that infection may cause weight gain in humans. It may explain the 'healthy obese', who have healthy BP and cholesterol levels despite being considered overweight.

The papers say that the discovery could lead to 'slimming vaccines', or antiviral drugs being used alongside dieting within the next five years.

Previous studies have shown a high prevalence of the virus in overweight people. For example, around 30 per cent of obese people have been estimated to have Ad-36 infection, compared with just 11 per cent of lean people.

WHAT IS THE RESEARCH?
The reports are based on US research that showed adult stem cells obtained from fatty tissue developed into fat cells when infected with Ad-36. The findings were presented at the 234th Annual Chemical Society meeting, in Boston this month.

The same team has linked Ad-36 with obesity in animals, and found a high prevalence of the virus in obese humans.

For the latest study, stem cells were obtained from a broad section of patients who had undergone liposuction.

Half of the stem cells were exposed to Ad-36 and the other half were left as control. After a week of growth in tissue culture, the virus caused the cells to convert to pre-adipose cells, rather than other cell types. The pre-adipose cells then accumulated lipids at an increased rate.

A specific gene in the virus that is thought to be involved in the mechanism was also pinpointed.

The research concluded that Ad-36 increases the number of fat cells and increases their fat content in humans, contributing to the development of obesity.

WHAT DO RESEARCHERS SAY?

Lead researcher Dr Magdalena Pasarica, from the Pennington Biomedical Research Center in Louisiana, said: 'We showed that human cells infected with this virus become fat cells.

'What we don't want people to say is that all obesity is caused by this virus. Obesity has multiple causes.'

Although the development of fat cells has been proven, the research does not provide a link between infection and obesity.

'Obviously we can't inject people with the virus and observe them, as we have done with animals. We have to identify the precise mechanism and the pathways in humans and correlate that against other data,' said Dr Pasarica.

'We can only say that it may trigger obesity in certain cases.'

The findings could lead to a vaccine or antiviral medication to help fight viral obesity in the future, she added.

WHAT DO THE EXPERTS SAY?
Dr David Haslam, clinical director of the National Obesity Forum, said the research did nothing to explain the obesity epidemic.

'It's unhelpful really,' he said. 'There are so many definite, concrete causes of obesity. We know that people are eating too much fat, doing less exercise, and watching too much TV.

'It does not explain why there is more obesity now than 50 years ago. Why weren't people getting fat from this virus then?'

Dr Haslam said the public should 'politely ignore' the study: 'We don't want people to think that they won't get fat if they wash their hands. That's just absurd. If it is true, it makes up only a tiny proportion of cases.'

INFORMING PATIENTS

• The main causes of obesity remain unchanged: poor diet and lack of exercise.
• There are still no reported cases of 'viral obesity' where other factors can be ruled out.
• Experts say patients should continue to exercise and eat healthily to avoid gaining weight.