The country's most pressing non-contagious health crisis seems to act like it is one. What does that mean for public health policy?

For help in understanding the rapid spread of obesity in the United States, one group of researchers has turned to the principles of physics. And what they have found is that it is spreading fast.

The team of scientists has recently published its findings in a paper called “Collective Behavior in the Spatial Spreading of Obesity.” Their analysis of the data using statistical physics methods found “correlations between the epidemic’s geography and food marketing and distribution patterns” and suggests that “individual habits may have negligible influence in shaping the patterns of spreading.”

In other words, the obesity crisis isn’t just happening on a person-by-person level. This isn’t about your individual weakness for supersizing. It looks, from a scientific perspective, like a systemic problem. And it is moving quickly. Obesity is a non-communicable disease that is spreading through this country like a virus.

The findings may have implications for public health policies aimed at reducing obesity, such as New York Mayor Michael Bloomberg’s proposal to ban large sugar-sweetened drinks or the “Let’s Move!” campaign spearheaded by First Lady Michelle Obama.

The researchers, including Lazaros Gallos and Hernán Makse of the City College of New York, looked at data including obesity and diabetes prevalence; physical activity; and the presence of food-related industries in the local economy, including restaurants, supermarkets, and food and beverage stores.

I asked Gallos to explain the research methodology and what the findings reveal about the way obesity is propagating across the country.

"The statistical physics methods can study the behavior of large ensembles of small interacting parts, e.g. the molecules in a gas," he writes in an email. "Although we cannot predict how an individual molecule will behave, we can make accurate calculations for macroscopic quantities, e.g. what is the temperature of this gas, as a result of collective behavior. Similarly, we can extend these methods to study how individual choices in real life result to collective behavior."

That's not to say, he continues, that you can't put down the fries of your own volition. But from a macro perspective, that one choice isn't the point. "Of course, every person in a society has the free will to adopt any opinion or behavior," he writes. "However, at the global level there are clearly observable trends, even though they represent the result of individual choices…. These individual choices can be much more dependent on global drivers, such as messages widely accepted by the current society norms, rather than a result of free will alone. The use of physics methods would then detect these general trends, in the same way that the seemingly chaotic motion of an enormous number of gas molecules results in a well-defined temperature."

Gallos says that his team’s analysis of the data showed a rapid geographic spread of obesity, with the main cluster centered in Greene County, Alabama. This area of the country is an obesity "hot spot," he says. But what is startling, and concerning, is the way that higher obesity rates have propagated over long distances, and how quickly and universally it is happening.

I asked him what the policy implications of the research might be. He cautiously says that it is an open question, but ventured some thoughts. "The results of our paper may seem to indicate that policies may be more successful if they address the 'obesogenic' environment created by the food industry and marketing forces directly," he writes. "Regulating the food industry (by e.g. making access to higher quality food easier, reducing or eliminating unhealthy food advertisements directed to children, taxing unhealthy processed food, etc., etc., as has been done with anti-smoking campaigns directed towards the tobacco industry) might help to deter the obesity epidemic faster than addressing the personal habits of each individual, one at a time."

The smoking analogy provides some real hope for the future, says Gallos. Since obesity seems to be spreading through social systems and societal norms, a similar full-court press effort to change those norms through a concerted set of policies might be able to effect positive change more quickly.

And cities might be the perfect place to start. "Cities are the place where most of the population lives," he says. "That is where trends start." The same forces that have spread obesity, says Gallos – societal and economic incentives to eat and get around in certain ways – could be used to reverse it. "It has spread through the social system," he says. "If you want to reverse the trend, that might be helpful."

Top image: travellight/

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