A person is more likely to be overweight if they live in close proximity to obese people, a US study has found.
The study, conducted at the University of South California, looked at the evidence of obesity being "socially contagious" - that is, the spreading of ideas and behaviour patterns through imitation and conformity.
Researchers looked at 3140 military families who were assigned to communities based on the needs of the military, not their own choice.
The study found that families sent to counties with higher obesity rates were more likely to be overweight than those placed in areas with lower obesity rates. The longer they remained there, the stronger the result.
"We were somewhat surprised," explained Dr Ashlesha Datar.
"Traditionally we think the built environment is what matters, or that people choose environments for a healthy lifestyle. But the findings show there's still a strong relationship to the community".
Dr Datar, from the University of Southern California, co-authored the study with economist Nancy Nicosia of RAND Corporation, American based global think tank.
In some states of the US, some 37.7 per cent of adults are obese. It's a similar story in Australia, where the adult population is 27.5 per cent obese and 35.3 per cent overweight - in total 62.8 per cent of the adult population.
"There are a sub-group of people [in Australia] who may be more health conscious," said Professor Louise Baur, a childhood obesity researcher from the University of Sydney.
"But there is a widening social disparity in adults and children in Australia."
She argues that Australia needs to pay more attention to balancing lived environment's affect on obesity by "increasing the availability of fresh healthy food" and "improving the walkability of neighbourhoods".
There also appears to be a large gap in health that correlates with environment. Australian adults were more likely to be obese if they lived in regional areas (68.8 per cent) as opposed to the city (60.1 per cent), and affluent Sydney suburbs were recently found to have far lower obesity rates than those that were less wealthy.
Children are also subject to this divide, with 56 per cent in outer regional areas overweight or obese, compared to 25 per cent in major cities.
This relationship between social environment was a major feature of the US research, with obesity results featured more strongly in 'off-base' families than those settled in the community.
Dr Datar believes it is important to remember that despite potential negative connotations, 'contagion' goes both ways - for both healthy and unhealthy behaviours.
"In San Francisco everyone rides bikes - this is also social contagion."
"People around you normalise your behaviour," said Professor Baur. "Environment has profound affect."
The findings could have significant impact on how doctors treat obesity. One article has already emerged, pointing out that the study's findings support the theory that treating an overweight parent is a more effective way of helping the child in the long term.
According to Professor Baur, this is not a new approach. "Parents influence children," she says. "Studies have shown that if the mum of the family loses weight then the child is more likely to".
