According to a new study in Economic Inquiry, an individual’s body weight depends not just on physiology and economic circumstances, but also on average body weight of the population at large. The study is the first to quantitatively model body weight distribution based on the combined outcome of economic, biological and social influences.
The findings complement those of a recent, high profile study that found direct evidence of social contagion of obesity within social networks. Although Burke and Heiland studied trends in the aggregate weight distribution, rather than following specific individuals over time, the evidence of person-to-person contagion provides strong support for their modeling approach.
“Behavior governing weight depends not just on health considerations but also on the desire to appear normal and attractive,” say authors Mary Burke and Frank Heiland. As a result, any change that causes average weight to increase, such as a decline in food prices, will lead to additional weight increases because the weight level considered “normal” will rise.
This is an example of a “social multiplier” effect. The authors find that their integrated model, describing the effects of economic and social change on a physiologically heterogeneous population, does a better job of explaining changes in the weight distribution over the past thirty years than do models based on economic change alone.
The authors also observe that a measure of weight dissatisfaction—the gap between average actual weight and average desired weight (controlling for weight, height, age, and education) fell significantly between 1989 and 2000, despite the fact that average weights increased over the same time period.
“Some people have objected to our claim that social norms governing acceptable body weight are on the rise, on the grounds that the idealization of thinness in popular culture appears as pronounced, if not more so, than ever,” say Burke and Heiland. “While we do not dispute this last fact, we believe there is strong evidence that a gap exists between the cultural imagery and the weights that most people consider acceptable for themselves and others.”
The research points to a long-term process of social adaptation to population-wide shifts in the body size distribution. The authors believe that this adaptation occurs with a time lag, and that the response to past declines in food prices may extend well into the future.
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