Diet, not lack of exercise, identified as main driver of obesity in global study

A major international study has concluded that diet, rather than insufficient physical activity, is the leading cause of rising obesity rates in developed countries.

Despite a boom in fitness trends, diet fads and wellness influencers, obesity continues to surge. In the United States alone, more than 40 per cent of adults were classified as living with obesity in 2023, according to the U.S. Centers for Disease Control and Prevention.

Seeking to understand what is fuelling the crisis, a global team of 65 scientists analysed data from over 4,500 adults living in 35 countries, encompassing a wide range of cultural and socioeconomic backgrounds. Participants consumed water infused with stable isotopes, allowing researchers to precisely measure their total daily energy expenditure, including calories burned through basic functions like breathing and heartbeat, as well as through physical activity.

Crucially, the researchers found that people from less physically active populations with higher obesity rates burned only marginally fewer calories than those from more active groups. In other words, a manual labourer or farmer did not significantly outpace an office worker in total energy expenditure.

“This large, international, collaborative effort allowed us to test long-standing assumptions,” said Professor Herman Pontzer, lead investigator and professor of evolutionary anthropology at Duke University. “It’s clear that changes in diet, not reduced activity, are the main cause of obesity in the U.S. and other developed countries.”

The findings support earlier research from Pontzer, which suggests that the human body adapts to increases in physical activity by reducing energy spent on other physiological processes, effectively keeping total calorie burn relatively constant.

Further analysis of the study data highlighted a strong link between the consumption of ultra-processed foods and increased body-fat percentages. These foods, which undergo extensive industrial processing, were more common in populations with higher obesity levels.

While the study does not diminish the importance of exercise, widely regarded as essential for heart health, mental wellbeing and reducing the risk of chronic disease, it does reframe the conversation around weight management.

The researchers stress that while staying active is vital for overall health, a healthy diet plays a far more critical role in preventing and reducing obesity.

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