Obesity In Wealthier Countries Driven By High-Calorie Diet, Not Lower Activity Levels, Study Suggests

Obesity rates across wealthier countries are rising, but contrary to media messages about couch potatoes and car culture, a new Duke University study suggests the primary culprit isnt a lack of physical activity — its increased calorie consumption.

A large international study conducted by researchers from Dukes Pontzer Lab, in the Department of Evolutionary Anthropology in Trinity College of Arts and Sciences, points to a high-calorie diet as the central driver of obesity in economically developed countries. Their findings were recently published in the Proceedings of the National Academy of Sciences (PNAS).

The study, led by Pontzer Lab principal investigator Herman Pontzer and Elon University assistant professor Amanda McGrosky, compared more than 4,200 adults from 34 populations across six continents, spanning a variety of lifestyles and economies, including hunter-gatherer, pastoralist, farming, and industrialized populations. To assess economic development, they also incorporated data from the United Nations Human Development Index for measures of lifespan, prosperity and education.

“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,” Pontzer said.

Participants ranged from 18 to 60 years old, and researchers measured each individuals total daily energy expenditure, body fat percentage, and body mass index (BMI). 

Despite longstanding assumptions that modern lifestyles are more sedentary and thus lead to weight gain, the data showed that people in developed countries often burn just as many — or more — calories as their counterparts in less industrialized regions. 

“Its clear that changes in diet, not reduced activity, are the main cause of obesity in the U.S. and other developed countries,” Pontzer said.

McGrosky, who served as lead investigator while a postdoctoral researcher at Duke, noted that total energy expenditure only marginally decreased with economic development and could not account for the substantial rise in body fat.

“This suggests that other factors, such as dietary changes, are driving the increases in body fat that we see with increasing economic development,” she said.

The authors said their findings should not be interpreted as a reason to downplay physical activity. Instead, they argue for a dual approach to public health that prioritizes both diet and exercise.

“Diet and physical activity should be viewed as essential and complementary, rather than interchangeable,” the authors write in the study.

They say future research will explore which specific dietary shifts in wealthier nations are most responsible for the surge in obesity.