A new study from Duke University challenges the popular belief that people are gaining weight because they are becoming less active.
Researchers found that in wealthier countries, people are still burning as much—or even more—energy each day compared to those in less developed countries.
This suggests that rising obesity rates are more closely tied to eating too many calories rather than not getting enough exercise.
The study was led by Duke’s Pontzer Lab, part of the Department of Evolutionary Anthropology, and was published in the journal PNAS. Scientists looked at data from over 4,200 adults aged 18 to 60 across 34 different populations on six continents.
These people came from all kinds of backgrounds, including hunter-gatherer communities, farming groups, and highly developed industrial societies.
To get a full picture, the researchers collected information on how much energy each person used daily, their body fat percentage, and their body mass index (BMI).
They also used the United Nations Human Development Index (HDI), which takes into account a country’s education levels, wealth, and life expectancy, to help measure how industrialized each population was.
Professor Herman Pontzer, who led the study, said that public health advice has often been confused about whether poor diet or lack of activity is more to blame for rising obesity rates. “This large international project allowed us to test those ideas, and the results are clear: it’s mostly diet,” he explained.
Lead researcher Amanda McGrosky, now a professor at Elon University, added that while there was a slight drop in energy use in more industrialized societies, it was not enough to explain the large increase in body fat. She said the real reason appears to be the way diets change in wealthier countries.
In short, the study shows that eating more calories is a bigger reason for obesity than being less active. But that doesn’t mean physical activity isn’t important. The researchers stress that both good nutrition and regular exercise are essential for health. They should be seen as partners, not substitutes, in the fight against obesity.
The team’s next goal is to figure out which parts of modern diets are most responsible for the increase in obesity. Understanding these details could help shape better public health advice and strategies to deal with this growing problem around the world.
The study is published in PNAS.
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