Is Obesity “Catching”? And Should It Be Diagnosed?

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A study published in The New England Journal of Medicine recently made headlines when it found that obesity can spread through social networks; in other words, that having friends who are obese raises a person’s risk of becoming obese himself.

Two-thirds of Americans are currently overweight, which is defined as having a body-mass index (BMI) of 25 or higher, and 31% of Americans are obese, with a BMI of 30 or higher.

The new findings about social networks and obesity came from a large, long-term study of heart disease called the Framingham Heart Study, in which over 12,000 of the residents of Framingham, Massachusetts, had their health tracked for three decades. This included having their body-mass index measured repeatedly over the years; participants had also provided information about their friends, siblings, spouses, and neighbors to help the study’s administrators keep track of them through the years in case their contact information changed.

By analyzing this information, researchers found that thin people and obese people tended to cluster together in social groups that extended to three degrees of separation (friends of friends of friends). Friendship seemed to have the biggest effect on obesity: A person’s likelihood of becoming obese went up by 57% if someone he considered a close friend became obese, and it went up by 171% if the two people identified each other as mutual friends. A person’s adult sibling or spouse becoming obese also increased his risk of becoming obese, raising it by 40% and 37%, respectively. People of the same gender had more of an effect on one another, and closeness of relationship was a better predictor of obesity than how close two people lived to one another. Similar trends were observed with weight loss, but since most of the study participants gained weight over time rather than losing it, the two groups were difficult to compare.

The study seems to provide evidence that people’s social networks are an important factor in their personal health.

Expert hypotheses about why this is the case include that friends influence one another’s perceptions of fatness—that if a close friend is obese, becoming obese yourself might not seem so bad. Another hypothesis is that friends are influenced by each other’s behaviors, and that people may pick up certain behaviors from friends who have a different body size. Finally, some experts felt that it was the spread of overweight and obesity as a social norm that accounted for these patterns.

Obesity, psychology, and nutrition researchers have suggested that, rather than using the study’s results to blame obese people for the spread of obesity, they can instead be used to help people come up with new ways to use social networks to fight overweight and obesity. For instance, instead of looking at obesity as a problem that an individual must struggle with alone, it may be more effective to find ways to treat both the obese person and the social network around him. Providing nutrition education in the workplace, for example, may be effective since many people are friends with their coworkers.

Another study about obesity, published in the August issue of Mayo Clinic Proceedings, looked at the medical records of almost 10,000 people who had been seen at the Mayo Clinic in Rochester, Minnesota. It found that only about one-fifth of obese people who saw a health-care provider at the clinic were formally diagnosed with obesity. The researchers also found that people who were formally diagnosed were 2.5 times more likely to be given a treatment plan, such as diet and exercise goals, by their health-care providers. People who were severely obese, had diabetes, or had sleep apnea were more likely to receive an official diagnosis of obesity.

The study’s principal investigator commented that people receive more guidance about weight management when doctors acknowledge obesity as a medical problem that can be diagnosed. Making formal diagnosis more of a norm may be another important tool in fighting the spread of obesity.

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