Is Obesity Contagious?

Contagious, of course, is the wrong word; it means transmitted by touch, and here we are considering only social and family proximity. A report in the New England Journal of Medicine describes 32-year data from the Framingham Heart Study that contained information on relatives and close friends of participants that could be used to track the member.

Clusters of obese people (using a BMI of 30 or above as the criterion) were found, which extended to three degrees of separation (e.g. a friend’s friend’s friend). A person’s chance of being obese increased by 57% if they had a friend who became obese in a given interval. The likelihood was 40% if a sibling became obese, and 37% if a spouse did.

Gender was important, too. If sampling was restricted to same-sex friendships (87% of the total), the probability of obesity increased by 71% if the friend became obese, while for friends of the opposite sex there was no significant association. This was similar for siblings. For sisters, the risk was 67%, for brothers 44%, while for siblings of opposite sex there was no increased risk. The obesity of a friend living far away was just as strongly associated as if the friend lived nearby. But neighbors’ weight had no influence.

This important study will provide much food for thought, both for the obese and non-obese. It seems that friends have an eminent influence on a person's risk of obesity. How about their risk of thinness, or other health-influencing conditions? It seems that so-called “network medicine” will become the latest discipline to provide us with the necessary lifestyle changes we must make to get/stay healthy. So, like father told you, choose your friends wisely!