It's often described as an epidemic, but rising obesity figures might have more in common with infectious diseases than we ever realised.

New research has added evidence to the idea that being in a social network with a higher level of obesity puts us more at risk of increasing our body mass index (BMI), almost as if we were 'catching' behaviours that make us put on weight.

A study conducted by a pair of US economists on families living on military bases has found that exposure to communities with higher rates of obesity is associated with an increase in BMI in parents and children.

There's been increasing interest over the past decade in understanding the way health-related behaviours spread through social networks.

Smoking is perhaps one of the more obvious examples, but studies have also explored the question of whether we are influenced to gain weight through our social ties.

Finding evidence one way or another is harder than you might think; it's hard to tease apart inherited factors from learned ones inside families, for one thing.

There's also the 'birds of a feather' factor, where we tend to associate with like-minded individuals. In other words, to what extent are we influenced by those in our social networks, compared with our choosing networks based on common behaviours?

That's what Ashlesha Datar of University of Southern California and Nancy Nicosia of the RAND Corporation set out to find.

To get around the problem of choosing social groups, the pair turned to a rather special type of community that assigns families to live close together from far and wide – the military base.  

Using data from the Military Teenagers' Environments, Exercise, and Nutrition Study (M-TEENS), the researchers combined details on 1,111 young adolescents and more than 1,300 parents who had been assigned to one of 12 military bases in the US.

The incidences of obesity varied across the counties where the bases were located, from 21 percent in El Paso County, Colorado, to 38 percent in Vernon County, Louisiana.

Measurements of the parents' and teens' BMIs revealed about a quarter of the teens and three quarters of the adults could be categorised as overweight or obese.

Once adjustments were made to take into account the effects of things like age, income, and even rank, it was found that members of a military family were more likely to have a higher BMI if they'd been assigned to a base in a country with greater obesity levels.

There were other indications that exposure to the local culture was behind this difference, such as the fact this relationship was stronger for families who lived off base in the surrounding community.

Teens who lived in close proximity to the base for more than two years were also more likely to have a higher BMI.

One explanation could be environment. It is possible that simply living in the area – with perhaps greater access to fast food or locations that discourage exercise – also plays a key role.

But the researchers are fairly confident that this isn't the case.

"While this study cannot definitively rule out the role of shared environments with the available measures, these findings suggest that other mechanisms may be at work," the authors write in their report.

Previous studies have focussed primarily on relationships between friends, neighbours, and family; studying the geographical networks is a step in a different direction making it hard to compare results.

But using military bases is a clever way to get around the whole self-selection issue that has plagued other research efforts.

The findings might not come as a great surprise, but they do provide much-needed evidence for the hypothesis that our social networks play a strong role in how we develop healthy and unhealthy habits.

Which shows when it comes to improving the health of our community, we're all in this together.

This research is published in JAMA Pediatrics.