You’re Not Lazy – But Your Diet Might Be Making You Fat

Think obesity is all about being inactive? Think again.

A global study from Duke University reveals that people in wealthier countries are just as active—sometimes even more so. The real problem isn’t how little we move, but how much we eat. After analyzing 34 populations across six continents, researchers found that as nations become richer, obesity rates climb without a corresponding decline in physical activity. The data flips a common belief on its head, pointing to diet—not laziness—as the key driver of the obesity epidemic.

Economic Growth and Rising Obesity

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, Alberto G. Bonomi, Pascal Bovet, Soren Brage, Maciej S. Buchowski, Nancy Butte, Stefan G. Camps, Regina Casper, Daniel K. Cummings, Sai Krupa Das, Sanjoy Deb, Lara R. Dugas, Ulf Ekelund, Terrence Forrester, Barry W. Fudge, Melanie Gillingham, Annelies H. Goris, Michael Gurven, Catherine Hambly, Annemiek Joosen, Peter T. Katzmarzyk, Kitty P. Kempen, William E. Kraus, Wantanee Kriengsinyos, Rebecca Kuriyan, Robert F. Kushner, Estelle V. Lambert, Christel L. Larsson, William R. Leonard, Nader Lessan, Marie Löf, Corby K. Martin, Anine C. Medin, Marian L. Neuhouser, Kirsi H. Pietilainen, Guy Plasqui, Ross L. Prentice, Susan B. Racette, David A. Raichlen, Eric Ravussin, Leanne Redman, Rebecca M. Reynolds, Eric B. Rimm, Susan Roberts, Asher Y. Rosinger, Mary H. Samuels, Srishti Sinha, J. Josh Snodgrass, Eric Stice, Ricardo Uauy, Samuel S. Urlacher, Jeanine A. Verbunt, Bruce Wolfe, Brian Wood, Xueying Zhang, Alexia J. Murphy-Alford, Cornelia J. Loechl, Jennifer Rood, Hiroyuki Sagayama, Dale A. Schoeller, Klaas R. Westerterp, William W. Wong, Yosuke Yamada, John R. Speakman, Herman Pontzer, null null, Lene F. Andersen, Linda Bandini, Stephan Branth, Niels C. De Bruin, Richard Cooper, Alice E. Dutman, Cara B. Ebbeling, Mikael Fogelholm, Tamara Harris, Rik Heijligenberg, Hans U. Jorgensen, David S. Ludwig, Eric Matsiko, Margaret McCloskey, Gerwin A. Meijer, Daphne L. Pannemans, Renaat M. Philippaerts, Jacob Plange-Rhule, Elisabet M. Rothenberg, Sabine Schulz, Albert Stunkard, Amy Subar, Minna Tanskanen, Ricardo Uauy, Rita Van den Berg-Emons, Ludo M. van Etten, Wim G. Van Gemert, Erica J. Velthuis-te Wierik, Wilhelmine W. Verboeket-van de Venne and Walter C. Willett, 14 July 2025, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2420902122

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