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A new nutrition study conducted by the International Atomic Energy Agency (IAEA) has found that the key driver of obesity in developed countries is increased calorie consumption, not decreased physical activity, as previously believed. The findings, published in the prestigious scientific journal Proceedings of the National Academy of Sciences , challenge the widely held belief that a sedentary lifestyle is the primary cause of the obesity epidemic.
"The Unclear Causes of Obesity in Rich Countries"
"Despite decades of research, the exact causes of the rise in obesity in industrialized countries remained unclear. The link between diet and physical activity remains debated," noted Herman Pontzer, professor of evolutionary anthropology and global health at Duke University and one of the study's authors. He emphasized that the IAEA database has enabled global efforts to test new hypotheses and reduce uncertainty in this area, which remains a major public health concern.
A large-scale global problem
According to researchers, nearly one in eight people on Earth was obese in 2022. Over the past three decades, obesity rates among adults have more than doubled, and among adolescents, they have quadrupled.
Obesity is a complex chronic condition characterized by excess accumulation of fat tissue in the body. It increases the risk of developing numerous non-communicable diseases, including diabetes, cardiovascular disease, and certain types of cancer.
Interestingly, obesity is virtually nonexistent in traditional and agricultural communities. This was previously attributed to the high physical activity of residents of such regions, but a new study challenges this theory.
Caloric intake vs. physical activity
Obesity is caused by an imbalance between energy intake and energy expenditure. Traditionally, experts have identified two key causes: overeating and insufficient physical activity. However, it has been discovered that low activity levels do not always directly impact total daily energy expenditure.
Previously, scientists lacked diverse and reliable data on dietary calorie intake, energy expenditure, and body composition. Most studies were conducted on non-industrialized populations and did not include measurements of body fat. Furthermore, information on food consumption was often collected only through surveys and general statistical data.
The double-labeled water method and the IAEA global database
To fill these data gaps, 68 researchers accessed the IAEA's global doubly labeled water database—a unique tool for measuring human energy expenditure using stable isotopes. The database contains data on 45 countries and various population groups. This resource has previously been used for energy metabolism studies and the revision of human nutritional standards.
How the study was conducted
Scientists analyzed the physical fitness of 4,213 adults aged 18 to 60 across six continents, encompassing 34 population groups with varying economic conditions and lifestyles. The results showed that even in industrialized countries, people demonstrated high energy expenditure, both related to physical activity and overall.
The main factor contributing to obesity was found to be excessive calorie intake , which the researchers assessed based on measurements of total energy expenditure and changes in body weight.
Implications for healthcare
"These results provide experts with new insights into the importance of nutrition in combating obesity," explained Cornelia Lechl, Head of the IAEA's Nutrition and Health Research Division. She noted that policies aimed at improving diet quality and reducing consumption of high-calorie and ultra-processed foods are likely to be more effective than simply encouraging physical activity .
Experts emphasize that such measures will be particularly relevant for countries with a high level of economic development, where access to high-calorie foods and highly processed foods is widespread.
Prospects
The IAEA study opens new avenues for developing global obesity strategies. It demonstrates that diet, not just physical activity, should be the primary focus. More broadly, the findings demonstrate the importance of a comprehensive approach to public health issues and evidence-based policymaking.
