New research suggests viruses could be the cause of the obesity epidemic

THE obesity epidemic seen in humans and their pets may be caused by more than rubbish diets and lack of exercise.

Some scientists think it may be due to a combination of issues, including viruses or something else that affects cells or organs.

This is opposed to the commonly held belief based on poor Western lifestyles that feature over-eating, little exercise and fatty foods.

Scientists' curiosity was triggered when they noticed laboratory rats and mice on strict diets had put on weight just as domestic pets and feral animals living around humans had.

They looked at more than 20,000 animals from 24 populations of eight species living in or around industrialised societies.

Scientists from nine research centres across the world found that in all cases, body weight was increasing.

"Surprisingly we find that over the past several decades, average mid-life body weights have risen among primates and rodents living in research colonies, as well as among feral rodents and domestic dogs and cats,'' they said.

The consistency of the findings in varying environments raises the intriguing possibility of non-diet-related factors being involved in weight gain.

In female mice they found an 11.8 per cent increase in body weight per decade from 1982, female cat weight had increased 13.6 per cent per decade, and male dogs had experienced a 2.2 per cent increase.

The scientists' work, published in the Proceedings of the Royal Society B, says that apart from obvious explanations such as over-eating and lack of exercise - there are many others, including the accumulation of endocrine-disrupting chemicals, and that obesity is of infectious origin.

The findings have implications for our understanding of the dramatic rise in human obesity. What cannot be explained is the rise in obesity in laboratory animals on controlled diets.

In Australia, veterinarians and the RSPCA have argued pet lovers may be loving their animals to death with over-feeding and little exercise.

Obesity rates for Australians also have doubled over the past 20 years, but mostly this has been seen as a lifestyle issue.

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