New Duke study finds obesity rises with caloric intake, not couch time

While many experts have offered that rising obesity rates are due to declining physical activity as societies become more industrialized, the findings show that people in wealthier countries expend just as much -- or even more -- energy daily. In an article recently published in PNAS, Duke researchers point instead to higher caloric intake as the primary driver, suggesting that diet rather than idleness plays the bigger role in the global obesity crisis.

"Despite decades of trying to understand the root causes of the obesity crisis in economically developed countries, public health guidance remains stuck with uncertainty as to the relative importance of diet and physical activity. This large, international, collaborative effort allows us to test these competing ideas. It's clear that changes in diet, not reduced activity, are the main cause of obesity in the U.S. and other developed countries," says Herman Pontzer, principal investigator with the Pontzer Lab and professor in the Department of Evolutionary Anthropology.

The researchers analyzed thousands of measurements of daily energy expenditure, body fat percentage and body mass index (BMI) from adults aged 18 to 60 across 34 populations spanning six continents. The more than 4,200 adults included in the study came from a wide range of lifestyles and economies, including hunter-gatherer, pastoralist, farming and industrialized populations. To further categorize the level of industrialization, they also integrated data from the United Nations Human Development Index (HDI) to incorporate measures of lifespan, prosperity and education.

"While we saw a marginal decrease in size-adjusted total energy expenditure with economic development, differences in total energy expenditure explained only a fraction of the increase in body fat that accompanied development. This suggests that other factors, such as dietary changes, are driving the increases in body fat that we see with increasing economic development," says Amanda McGrosky, a Duke postdoctoral alumna and lead investigator for the study who is now an assistant professor of biology at Elon University.

The researchers hope the study helps clarify public health messaging and strategies to tackle the obesity crisis and explain that the findings do not mean that efforts to promote physical activity should be minimized. Instead, the data support an emerging consensus that both diet and exercise should be prioritized. "Diet and physical activity should be viewed as essential and complementary, rather than interchangeable," the study notes. They will next work to identify which aspects of diet in developed countries are most responsible for the rise in obesity.