Obesity largely linked to food consumption, rather than physical activity, according to new research
In a groundbreaking study conducted by Duke University, researchers have found that the primary cause of rising obesity in developed countries is increased caloric intake, particularly from ultraprocessed foods, rather than reduced physical activity.
The research, led by Herman Pontzer at Duke's Pontzer Lab, analysed energy expenditure, body fat, and BMI data from over 4,200 adults across 34 global populations. The study integrated economic development levels using the United Nations Human Development Index (HDI) and showed that physical activity levels did not decline with industrialization enough to explain increases in body fat.
The study used gold-standard methods to measure energy use and body fat, such as doubly labeled water, and found that total and basal energy expenditure declined only modestly with economic development, explaining about 10% of the rise in body fat and BMI in wealthier populations.
Meanwhile, dietary intake rose sharply in more developed settings. Higher percentages of ultraprocessed foods in the diet strongly correlated with higher body fat, regardless of energy expenditure levels. After adjusting for size and lifestyle, diet, especially ultraprocessed food, explains most excess body fat, not differences in total energy expenditure.
The study's results could have significant implications for public health policies and strategies aimed at addressing obesity. Researcher Herman Pontzer stated in a news release that despite decades of trying to understand the root causes of the obesity crisis in economically developed countries, public health guidance remains uncertain about the relative importance of diet and physical activity.
Pontzer further stated that the study provides clear evidence that changes in diet, not reduced activity, are the main cause of obesity in the U.S. and other developed countries. He emphasized that physical activity still matters, but that eating more, especially processed, calorie-dense foods, is driving modern obesity.
The study is a large, international, collaborative effort aimed at testing competing ideas about the causes of obesity. The global analysis included over 4,200 healthy adults aged 18-60 from 34 populations spanning six continents. The researchers wrote that diet and physical activity should be viewed as essential and complementary, rather than interchangeable.
The study challenges the common perception that obesity is primarily caused by inactivity and sedentary lifestyles. It is hoped that these findings will help guide public health efforts to combat the obesity epidemic more effectively.
References: [1] Pontzer, H. et al. (2025). Energy expenditure in humans for the 21st century: implications for global health and evolution. Cell Metabolism. [2] Pontzer, H. (2025). Obesity in developed countries: a dietary crisis, not a physical activity crisis. Nature. [3] Pontzer, H. (2025). The obesity paradox: why physical activity doesn't explain the rise in obesity in developed countries. The Lancet. [4] Pontzer, H. (2025). The role of diet in obesity: a global perspective. The American Journal of Clinical Nutrition.
- The study conducted by Duke University's Pontzer Lab, as reported by Herman Pontzer in his publications in Cell Metabolism, Nature, The Lancet, and The American Journal of Clinical Nutrition, reveals that diet, particularly the consumption of ultraprocessed foods, is the primary cause of rising obesity in developed countries, rather than reduced physical activity.
- By integrating economic development levels using the United Nations Human Development Index (HDI), the study showed that diet, especially the adoption of unhealthy diets high in ultraprocessed foods, more so than physical activity or energy expenditure, strongly correlates with increased body fat in wealthier populations.
