The nation's obesity epidemic is striking all groups of Americans, affecting those with more education and those with less education, as well as all ethnic groups, according to a new analysis that challenges prevailing assumptions about the reasons why the nation is getting heavier.
While some differences in weight are evident between groups based on race and education levels, all Americans have been getting fatter at about the same rate for the past 25 years, even as the nation saw increases in leisure time, increased availability of fruit and vegetables, and increases in exercise.
Since 1970, the average per capita consumption of calories of Americans has risen by about 20 percent, while at the same time there has been a sharp drop in the cost of food as a proportion of disposable income, according to a report published online by the journal CA: A Cancer Journal for Clinicians.
"Not only has food been getting cheaper, but it is easier to acquire and easier to prepare," said Roland Sturm, lead author of the report and a senior economist at RAND, a nonprofit research organization. "It's not just that we may be eating more high-calorie food, but we are eating more of all types of food."
Many factors have been blamed for a growing incidence of obesity in the United States, including fast food, suburban sprawl, the size of prepared meals, poverty, affluence, a lack of exercise and a shortage of access to healthy foods.
Analyzing economic factors that contribute to obesity, Sturm and co-author Ruopeng An of the University of Illinois at Urbana-Champaign found that weight gain was surprisingly similar across sociodemographic groups and geographic areas, rather than specific to some groups. The findings suggest that the cause of obesity is driven by environmental factors that affect all groups, not just a few.
The RAND researchers say that Americans now have the cheapest food in history, when measured as a fraction of disposal income. During the 1930s, American spent about one-quarter of their disposal income on food, dropping to one-fifth during the 1950s. Today, Americans spend about one-tenth of their disposable income on food.
"Not only has the cost of food dropped, but it has become even more available," An said. "So a smaller share of Americans' disposable income now buys many more calories."
The decline of food expenditures relative to income becomes more dramatic when considering quality factors, such as greater convenience, reduced time needed for preparation, increased variety and the ubiquitous availability of food.
Sturm and An say that effective economic policies to curb obesity remain elusive.
Imposing taxes on foods with low-nutritional value could nudge behavior toward healthier diets, as might subsidies or discounts for healthier foods. But political and popular support for such approaches has been low.
For example, Denmark imposed a tax on foods high in saturated fats in 2011, only to repeal the move a year later. In the United States, there have been numerous legislative proposals to tax soft drinks or junk food, but no meaningful plans have passed to date.
"The high cost of healthy food may not be the problem as far as obesity is concerned, rather it is the excess availability and affordability of all types of food," Sturm said. "We need to consider strategies that replace calorie-dense foods with fruits and vegetables, rather than just add fruits and vegetables to the diet."