Duke scientists analyzed global data and found that obesity isn’t rising because we’ve stopped moving — it’s because we’re eating more.
By Margo Lakin, Duke University
A new study from Duke University’s Pontzer Lab, part of the
Department of Evolutionary Anthropology at Trinity College of Arts &
Sciences, explores how economic growth relates to obesity, daily calorie burn,
and lifestyle changes around the world.
Many experts have long believed that rising obesity rates
are tied to people being less physically active as societies become more
industrialized. But the research tells a different story. According to the
findings, people living in wealthier countries actually burn as much or even
more energy each day.
Published in PNAS, the study points to increased
calorie consumption—not inactivity—as the leading factor behind climbing
obesity rates. The researchers suggest that what people eat, rather than how
little they move, is the more significant contributor to the global obesity
problem.
Diet vs. Exercise: A Global Test
“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.
To reach these conclusions, the team examined over 4,200
adults between the ages of 18 and 60 across 34 populations on six continents.
The individuals represented a broad range of economic and cultural settings,
including hunter-gatherer groups, herding communities, farmers, and people
living in industrialized nations. The researchers also used data from the
United Nations Human Development Index (HDI), which includes measures of
education, income, and life expectancy, to help classify the degree of economic
development in each population.
Economic Development and Body Fat
“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.
Reference: “Energy expenditure and obesity across the
economic spectrum” by Amanda McGrosky, Amy Luke, Leonore Arab, Kweku Bedu-Addo,
et al. 14 July
2025, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2420902122
