For years, public health debates have revolved around whether obesity is caused more by lack of physical activity or by poor diet. Now, a groundbreaking international study has delivered a clear answer: it’s not exercise, it’s diet.
Drawing on data from the International Atomic Energy Agency’s (IAEA) Doubly Labelled Water Database, researchers have revealed that increased calorie intake is the dominant driver of obesity in wealthier, industrialized societies, not reduced physical activity.
“Despite decades of trying to understand the root causes of the obesity crisis in economically developed countries, the relative importance of diet and physical activity has remained uncertain,”
Herman Pontzer, professor of evolutionary anthropology and global health at Duke University and one of the article’s authors said,
“The IAEA’s Doubly Labelled Water Database has enabled a collaborative global effort to not only test these ideas, but also resolve the uncertainty around a pressing public health challenge.”
Why Obesity Keeps Rising Globally
Obesity has become one of the most pressing global health issues. By 2022, nearly one in eight people worldwide were living with obesity. In just 30 years, rates have more than doubled among adults and quadrupled among adolescents. This condition dramatically raises the risk of diabetes, heart disease, and cancer.
Interestingly, obesity remains rare in farming and traditional societies, where physical activity levels are higher. This led many to assume that inactivity was the main culprit. But the new findings challenge that narrative by showing that even in more active societies, calorie intake is the real tipping point.
What the Research Found
The study analyzed 4,213 adults across six continents, using detailed energy expenditure and body composition data from 34 populations. Researchers found that people in industrialized economies actually burn more energy on average. But once adjusted for larger body sizes, the difference in energy expenditure explained only about 10% of the rise in obesity rates.
In contrast, higher calorie intake was strongly linked to weight gain. In short, the imbalance between calories consumed and energy burned points directly to diet as the dominant driver.
For public health professionals and nutrition specialists, these findings offer novel insights on the importance of diet. Policies which focus on improving diet quality and reducing the consumption of high-calorie, ultra-processed foods are likely to be more effective in combating obesity than those centred solely on increased physical activity, explained Cornelia Loechl, Head of Nutritional and Health-related Environmental Studies in the IAEA Division of Human Health and one of the article’s authors. “More broadly, these insights are a testament to the impactful scientific research the IAEA’s human health databases enable.
What This Means Going Forward
The takeaway is clear: while exercise remains important for overall health, it cannot compensate for the effects of consistently high-calorie, ultra-processed diets. For policymakers and health experts, this research underscores the need to prioritize food quality and calorie reduction strategies over campaigns that focus only on getting people to move more.
The study, published in the Proceedings of the National Academy of Sciences, has already sparked global attention. Since its release, the article has been read more than 72,000 times and covered by over 165 international media outlets, marking it as one of the most influential contributions to the obesity debate in recent years.