Among the American public and even some policymakers, it has become conventional wisdom that poverty, a dearth of supermarkets, reduced leisure time, and insufficient exercise are key forces behind the U.S. obesity epidemic.
Conventional wisdom is an unreliable guide, however, and in this case, much of it is wrong: The epidemic actually coincides with a falling share of income spent on food, wider availability of fruits and vegetables, increased leisure time, and more exercise among the general population.
Of course, there are differences between individuals, but we need to explain the change in obesity over time, not why people differ. Some differences in body mass index (BMI) are associated with genetic makeup. But genes haven’t changed in the past 50 years, so differences between individuals don’t explain trends.
Data from a new analysis of this issue indicates that the same argument applies to other characteristics, such as geography. Southern hospitality’s heavy food hasn’t caused the obesity epidemic any more than an active Colorado lifestyle has prevented it. There are differences at a given point in time, but the trend is the same, as shown in the figure below.
Percentage of Population with a BMI Over 25 in California, Colorado, and Mississippi
SOURCE: Calculations based on Behavioral Risk Factor Surveillance Survey; smooth trend adjusted for 2010 demographics.
Increases in obesity have also been surprisingly similar by level of education and by racial/ethnic group, as the following figures show.
Increase in Average BMI Nationwide, by Highest Education Level Achieved
SOURCE: Calculations based on Behavioral Risk Factor Surveillance Survey; smooth trend adjusted for 2010 demographics.Continue reading…