What is the story?
The obesity epidemic sweeping the nation may not be the result of poor diet and lack of exercise after all, according to media reports that suggest that it could be caused by a virus.
The papers reported that US researchers had identified a virus which causes weight gain in animals, supporting the theory that 'fat is infectious'.
This could mean that the recent increases in obesity are the result of people 'catching' obesity like a cold. It could also mean that it is possible to develop a vaccine for preventing obesity, the papers claimed.
They advised that people wanting to stay thin should ensure that they eat healthily, exercise - and wash their hands.
What is the research?
The media reports are based on research looking into the effects of infection with human adenoviruses on the adiposity of chickens.
Previous studies have shown that infection with human adenovirus-36 (Ad-36) produces obesity in chickens, mice and non-human primates.
Researchers tested to see if infection with three of the other 51 types of human adenovirus would produce obesity in chickens. They infected 54 three-week-old chickens with either human adenovirus-2 (Ad-2), human adenovirus-31 (Ad-31), human adenovirus-37 (Ad-37) or a placebo.
The researchers found that after three weeks, chickens infected with Ad-37, but not Ad-31 or Ad-2, were heavier and had three times as much visceral fat and twice as much total body fat as the controls, even though their food intake was no higher.
The researchers concluded that Ad-37 should be added to the list of human viruses that cause weight gain in animals and suggested that it does this by reducing the metabolic rate.
What do the researchers say?
Lead researcher Dr Leah Wigham, from the department of medicine and nutritional sciences at the University of Wisconsin, said that this research showed that Ad-37 should be added to the list of adenoviruses that are known to be obesogenic.
'The first evidence for a viral contribution to obesity was gathered in the late 80s when Dr Nikhil Dhurundbar found a link between a chicken virus and obesity in humans,' she said.
'Since then two human adenoviruses have been shown to promote adiposity in animals. Now, we've shown that another virus - Ad-37 - also causes obesity in chickens. But, as promising as the evidence is, we don't have cause and effect data.'
She added that identifying the specific adenoviruses that promote obesity was the first step towards developing a vaccine against obesity.
In the meantime, she recommended that people should take the same precautions as they would during cold and flu season to avoid infection.
What do other experts say?
Professor Edwin Gale, who has researched the possibility of a viral basis for type-1 diabetes at North Bristol University, was sceptical about the research.
'Obesity has thermodynamic causes. It results from excess intake over output of calories so the idea that this virus could cause excess adipose tissue deposition without affecting food intake is extremely funny,' he said.
'It is an interesting observation which might be worth pursuing, but at least in so far as human obesity is concerned, we don't need to invoke a virus.'
Professor Stephen Bloom, from the Endocrine Research Unit at the Hammersmith Hospital, who researches obesity, said that there was no theoretical reason why a virus should not attack an appetite regulatory part of the brain and thereby cause obesity.
However, he said that it was very unlikely that a virus was the main cause of the epidemic.
'There are very good reasons why we are all getting fatter. This is not the answer to the fat maiden's prayer,' he said.
Am J Physiol Regul Integr Comp Physio 2006; 290: R190-4
WHAT THE PAPERS SAID
"Virus could be obesity trigger" - The Sunday Times
"Obesity 'can be caught like a cold'" - The Daily Telegraph
"Obesity can be caught from a virus, scientist says" - The Times
- A third human virus has been found to produce obesity in chickens, by a small team of researchers in the US.
- Although they hope a vaccine against obesity could one day be developed, other experts are sceptical.
- A viral cause of obesity is a long way from being proved.
- Healthy eating and frequent exercise are the only ways to prevent obesity.