Obese friend is bad for your health, says study

HAVING an obese friend dramatically increases the risk of becoming similarly fat, according to a study released yesterday.

Obesity is “socially contagious,” spreading from person to person in a social network, researchers said.

The study, published in the New England Journal of Medicine, found that if one person becomes obese, those closely connected to him or her have a greater chance of becoming obese themselves.

Surprisingly, the greatest effect was seen not among people sharing the same genes or household, but among friends.

When a person becomes obese, the chances that a friend will also become obese increases by 57%, Harvard Medical School and University of California researchers found.

Their siblings have a 40% increased risk, and their spouse a 37% increased risk.

However, a neighbour is not at any increased risk, unless they are also friends.

The researchers analysed data over 32 years for 12,067 adults who underwent repeated medical assessments as part of a heart study. They were able to map the interconnected social network using information that listed participants’ family changes and contact information for their closest friends.

The map, which included the adults’ body-mass index, revealed the network grew heavier over time, consistent with other studies that have found an obesity epidemic in the US.

But it also immediately showed distinct clusters of thin and heavy individuals which could not be solely attributed to the forming of ties among people of comparable weights.

Nicholas Christakis, co-author of the study and a professor at Harvard Medical School’s department of healthcare policy, said: “It’s not that obese or non-obese people simply find other similar people to hang out with. Rather, there is a direct, causal relationship.”

The study found obesity among friends could not be explained by similarities in lifestyle and environment, such as people eating the same foods together.

Prof Christakis said: “People come to think it is okay to be bigger since those around them are bigger, and this sensibility spreads.”

Co-author, James Fowler of the University of California, said: “It’s important to remember that we’ve not only shown that obesity is contagious but that thinness is contagious.”