The ‘social contagion’ of obesity

Subconsciously, you are affected by what people do around you

YOUR social circle might be the reason you are overweight, a study has suggested. Experts have warned that obesity can spread through communities like a “social contagion”.

Researchers studied hundreds of military families – who can’t choose where they live – across the US. Their results revealed that if you move to an area with a high rate of obesity, it increases your risk of becoming obese.

The University of Southern California researchers said people adopt behaviours of others subconsciously.

Dr Ashlesha Datar and colleagues recruited families of US Army personnel at 38 military bases across the country. A total of 1314 parents and 1 111 children participated, whose rates of obesity were reflective of the national rates.

One in three adults in a typical US county is obese and in the UK about a quarter of adults and a fifth of children are obese.

Some of the bases were in counties with higher rates of obesity. Rates ranged from 21 to 38%.

The study showed that, when assigned to bases in counties with higher rates of obesity, residents were more likely to become overweight.

For every percentage-point increase in obesity rate of local people, the chances that a teenager would be obese went up by 4 to 6%, while the odds that a parent would be obese went up by 5%. The longer the families lived there, the more likely they were to see the weight pile on.

“Social contagion in obesity means that if more people around you are obese, then that may increase your own chances of becoming obese,” said Datar. “Subconsciously, you are affected by what people around you are doing.”

The researchers accounted for environmental factors that could have explained the obesity rate, such as if there was a lack of gyms but lots of fast food restaurants. Despite this, the obesity connections were still apparent, suggesting other factors were to blame.

“We cannot say for sure that we accounted for everything that might influence eating and exercise behaviours,” Datar said. “But we did account for things that researchers in this field typically measure and found that shared environments did not play a critical role in explaining our results.”

Co-author Dr Nancy Nicosia, a senior economist at Rand Co-operation, said: “Although we could not measure social contagion directly, our findings support a role for social contagion in obesity.”

Obesity can be caused by many variables and previous research shows that living in certain communities carries a higher risk of obesity than living in other communities.

But the association has been challenging for scientists to explain.

One possibility is that people with similar interests and backgrounds tend to locate in similar areas.

Another explanation may be that people are all influenced by the shared environment, such as opportunities for exercising and healthy eating. A third explanation is that obesity is transmitted through social influence.

“Assessing the relative importance of these explanations has been a challenging task and yet is important for designing effective policies to address obesity. Our study sought to take on that challenge,” said Datar.

Obesity is defined as an adult having a BMI of 30 or over. A healthy person’s BMI – calculated by dividing weight in kg by height in metres, and the answer by the height again – is between 18.5 and 24.9.

Among children, obesity is defined as being in the 95th percentile. Percentiles compare youngsters to others their age. For example, if a 3-monthold is in the 40th percentile for weight, that means that 40% of 3-month-olds weigh the same or less than that baby.

About 58% of women and 68% of men in the UK are overweight or obese. The condition costs the National Health Service about £6.1billion (R117bn), out of its £124.7bn budget, every year. This is due to obesity increasing a person’s risk of a number of life-threatening conditions.

Such conditions include type 2 diabetes, which can cause kidney disease, blindness and even limb amputations.

Obesity also raises the risk of heart disease, which kills 315 000 people every year in the UK – making it the number one cause of death.

Carrying dangerous amounts of weight has also been linked to 12 different cancers.

Among children, research suggests that 70% of obese youngsters have high blood pressure or raised cholesterol, which puts them at risk of heart disease.

Obese children are also significantly more likely to become obese adults. And if children are overweight, their obesity in adulthood is often more severe.