About the study

For the study, which was published in PNAS, researchers analyzed data from more than 4,200 adults across 34 countries, ranging from Tanzanian hunter-gatherers and farming communities to office workers in industrialized nations. Participants drank water containing isotopes that later appeared in their urine, a method that allowed researchers to precisely measure total daily expenditure over the course of a week.

"This allows us to get a really accurate measure of how many calories people burn per day over the course of about a week," said Herman Pontzer, a professor of evolutionary biology and global health at Duke University who led the study.

When the research team adjusted for body size, they found that people from countries with higher obesity rates burned only slightly fewer calories than people from countries with lower obesity rates.

These differences in energy expenditure didn't contribute much to the differences in obesity rates among populations, Pontzer said.

The findings align with Pontzer's earlier research, which suggests that the human body maintains a stable energy budget by compensating in other areas. "So if we burn more of our energy every day on physical activity, on exercise, after a while our bodies will adjust and spend less energy on the other tasks that we sort of don't notice going on in the background," Pontzer said.

Discussion

The study's findings challenge a long-held assumption that sedentary lifestyles are the primary cause of global weight gain.

"This does sort of really fly in the face of what a lot of us anecdotally assumed was driving a lot of the weight gain and obesity today," said Deirdre Tobias, an obesity and nutritional epidemiologist at the Brigham and Women's Hospital in Boston and the Harvard T.H. Chan School of Public Health. Tobias was not involved in the study but praised its design.

"For decades we've been telling Americans that you're lazy, it's your fault, you're not moving enough, you're eating too much," Mozaffarian said. "And I think what this study shows is that there's really complicated biology happening and that our food is driving this."

The research doesn't discount the benefits of exercise. Physical activity remains critical for mental and physical health. Still, Ponzer said if the goal is to reduce obesity, the message needs to shift. The focus, he argued, should be on what we eat — not how much we move.

"If we want to tackle obesity," Ponzer said, "the public health message should focus on changing what's on our plates."

Advisory Board's weight-related resources

To help you address the potential side effects associated with weight management drugs, Advisory Board offers several resources:

This expert insight outlines the five biggest questions about weight-management drugs and their answers. Similarly, this expert insight addresses what headlines get wrong about weight-management drugs and what healthcare leaders should know instead.

Radio Advisory's Rachel Woods has also covered GLP-1 drugs on the podcast, discussing the potential future of these drugs and how they could help — or hurt — health systems' finances. Other useful resources include this expert insight on the five catalysts that will impact the future of obesity care and this research on four key elements of comprehensive obesity care.

Our weight management and obesity care resource library can also help leaders understand the current care landscape, manage innovations, and prepare for transformations in care.