(12-11-10) Obesity rate will rise to 42% of the population based on contagion

Obesity rates in the United States, which some health experts have suggested
may be stabilizing at about 34%, will continue to rise until at least 42% of
American adults are obese, according to a new model that projects the increase
based on "social contagion."

The social contagion hypothesis garnered widespread attention in 2007 when
researchers from UC San Diego, documented that obesity can spread through a
social network -- just like viruses spread -- because people "infect" each
other with their perceptions of weight. That study was published in the New
England Journal of Medicine, and subsequent research has confirmed the validity
of the social contagion theory.

In a paper published Thursday in the journal PLoS Computational Biology,
Harvard scientists applied a mathematical model of social contagion to 40 years
of data from the Framingham Heart Study, a study that has followed more than
5,000 adult residents of Framingham, Mass., since 1948 to assess their heart
health. Among the participants of that study, obesity increased from 14% in the
1970s to 30% in 2000 and continues to increase. Based on that data, the rapid
upswing in obesity rates is due largely to social-network influence, said the
authors of the new study. But, they noted, any subsequent rise in obesity rates
will be slower than it has in the past. It may take another 40 years to reach
that 42% obesity mark.

Non-social factors that lead to obesity -- such as access to unhealthy food
and sedentary lifestyles -- are still much more important to the spread of
obesity, the authors said. The social-contagion factor is a more recent factor.


Being surrounded by more obese people leads to increased social acceptability
of obesity which leads to a higher rate of becoming obese, the authors wrote,
". . .creating a positive feedback mechanism and a continuously increasing
obese fraction of the population. It has been suggested that changing social
norms that stigmatized smoking may have led to its decline, and just the
opposite may be true for obesity."

A non-obese American has a 2% chance of becoming obese in any given year, the
study found. The number rises by 0.4% with each obese social contact. So, if
you have five obese friends, that doubles your risk of becoming obese. The
study found that the rate of recovery from obesity -- about 4% per year -- has
not changed.

Source: Shari Roan, Los Angeles Times

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