A study has revealed that the cause of obesity affecting over 1 billion people worldwide is due more to overeating than a lack of exercise. This research challenges the common belief that obesity is primarily caused by insufficient physical activity and suggests the need for policy interventions to reduce calorie (energy) excess.
A research team led by Professor Herman Pontzer from Duke University analyzed the energy consumption of thousands of people living across six continents with diverse economic levels and lifestyles and published the findings on 14th (local time) in the Proceedings of the National Academy of Sciences (PNAS) of the United States.
The research team analyzed participants' calorie consumption. The method involved measuring the ratio of oxygen and hydrogen isotopes expelled as urine after drinking water to accurately measure calorie consumption. Additionally, they calculated the calories burned through actual physical activity, excluding energy required for basic metabolism and digestion, such as respiration and body temperature regulation.
The analysis found that groups belonging to more economically advanced societies tend to have slightly lower energy consumption on average, even when considering body size. However, this difference was not large enough to explain the stark differences in obesity rates. Energy consumption indicates how much the body is utilized.
The research team indicated that the contribution of the difference in energy consumption to explaining the correlation between economic development levels and obesity indicators is only 10%, with the remaining 90% ultimately attributed to excess intake.
Co-author Amanda McGrosky, a professor at Elon University, noted, "The difference in energy consumption between groups is minimal, and there is significant variation between regions," explaining that "most of this difference stems from variations in basal metabolic rates rather than physical activity."
However, there have been criticisms in academia regarding limitations in this research. Dr. Vanessa Oddo, an epidemiologist at the University of Illinois who did not participate in the study, pointed out that "these findings align with the current academic consensus that increasing energy intake is a major cause of obesity," but she also remarked, "Since this research is based on indirect measurements and modeling, there are limitations to establishing causality."
Jeff Goldsmith, a biostatistician and professor at Columbia University, acknowledged, "The use of objective energy consumption and body fat percentage measurements is commendable," but also expressed concern that "data from hunter-gatherer societies or horticultural societies is limited to a few dozen individuals, raising concerns about sample imbalance."
In fact, since the research team did not directly investigate individual participants' diets, they could not precisely determine how dietary habits in economically developed societies lead to obesity. However, a trend was observed where groups that typically consume high-calorie, ultra-processed foods had higher body fat percentages on average.
Professor McGrosky stated, "Further research is necessary, and these results do not negate the importance of exercise." He added, "Physical activity is crucial for overall health," suggesting that "the impact of exercise on overall energy expenditure may not be as significant as previously thought."
References
PNAS (2025) DOI: https://www.pnas.org/doi/full/10.1073/pnas.2420902122