What Contributes More to Obesity-Poor Diet or Lack of Exercise? Study Sheds Light - Video

A study published in the journal Proceedings of the National Academy of Sciences (PNAS), reveals that diet-not declining physical activity-is the key driver of rising obesity rates in economically developed countries.

Led by Herman Pontzer, professor in Duke’s Department of Evolutionary Anthropology, the study analyzed data from more than 4,200 adults aged 18 to 60, across 34 populations on six continents. These participants represented a broad range of lifestyles, from hunter-gatherer and farming communities to industrialized societies. The researchers collected extensive measurements of daily energy expenditure, body fat percentage, and body mass index (BMI) to examine how lifestyle and economic development impact energy use and obesity.

To assess the level of industrialization, the team also incorporated the United Nations Human Development Index (HDI), which accounts for factors such as lifespan, education, and economic prosperity. Despite expectations, the study found that people in wealthier countries expend as much — or even more — energy daily than those in less industrialized settings.

“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,” said Pontzer.

The researchers emphasize that while diet is the dominant factor in obesity, this doesn’t mean physical activity should be neglected. “Diet and physical activity should be viewed as essential and complementary, rather than interchangeable,” the study notes.

Reference: “Energy expenditure and obesity across the economic spectrum,” Amanda McGrosky et al., Proceedings of the National Academy of Sciences, 14 July 2025 DOI: 10.1073/pnas.2420902122