Obesity may be contagious

With rates of obesity in Australia only marginally behind the United States and tracking at the same pace, mathematical and social modelling on the projection of obesity rates in America is sobering reading for Australians.

The most recent statistics on the weight and health of the Australian population paints the grim picture of one in four adults classified as obese (defined as a body mass index above 30 kg/m²). When overweight is added to this, 68% of adult Australians are likely carrying more weight than what is good for them. These rates have been consistently rising for the last three decades and do not appear to show any signs of slowing.

A research team from Harvard University has applied complex mathematical modelling, derived from long running diet and health studies, to determine how obesity rates could look like in the United States in the future. As Australia closely matches and tracks the United States for obesity rates, and has a similar standard of living, then forecasts from this modelling would have currency for Australians.

The bottom line is that obesity rates will likely reach a peak of 42% of the population within 40 years. This result on its own is probably not so surprising, but the interesting finding that came from the research was the factors most likely to predict if a person would become obese.

The more friends a person has who are obese, the greater their own chance of becoming obese is. To put some hard numbers to the finding, each adult was found to have a 2% chance of becoming obese in any given year. But for every obese friend a person had, their own risk of becoming obese increased by 0.5 percentage points. So someone with a social circle of six obese friends would have a risk of 5% of becoming obese themselves.

Although another recent study found that a single gene mutation heightened the risk of obesity by up to 67 percent, genetics cannot explain the skyrocketing obesity trend. Lifestyle choices or other features of modern life must be contributing as well. And some researchers have even proposed that infections of gut bacteria account for some cases of obesity.

Christakis and political scientist James Fowler of the University of California, San Diego, analyzed 32 years' worth of recent records from 12,067 participants in the Framingham Heart Study, which has followed the health of residents of a small Massachusetts town and their offspring every four years since 1948.

Aside from listing their spouses and family members at each follow-up, participants gave names of close friends who would likely know their future whereabouts; more than 70 percent of these were also included in the study, creating a dense social network suitable for identifying epidemiclike effects.

When two people each listed the other as a friend and one of them packed on the pounds, the second person was 171 percent more likely to become obese. However, if only one member of the pair considered the other a friend, obesity was more likely to spread only to the person holding that view.

A person whose friends had obese friends carried an added 20 percent risk of obesity, which fell to 10 percent for friends of the third degree. In comparison, a chunky sibling increased the risk by 40 percent and a spouse by 37 percent.

Geographic location had no bearing on the results: A portly neighbor had no effect, but a friend who gained weight and lived far away still appeared to raise the risk of obesity. People of the same sex also had a stronger impact on one another.

So, arn't you lucky to have me as a friend ;)