A major international study is upending deeply held beliefs about obesity, concluding that excess calorie consumption—not a lack of physical activity—is the primary cause of the obesity epidemic in the United States and other developed nations. The findings, published in the Proceedings of the National Academy of Sciences (PNAS) this week, suggest that decades of public health campaigns blaming sedentary behavior for rising obesity rates may be missing the real culprit: modern diets.
Obesity has been characterized as a growing health emergency, both globally and in Thailand, with the World Health Organization warning of associated consequences such as Type 2 diabetes, heart disease, and increased mortality. For years, the narrative was that the comforts of the modern world—office jobs, televisions, cars—had made people dangerously inactive. However, the new research offers a striking counterpoint, shifting the focus away from exercise and toward the food environment [PNAS, 2025].
Analysing energy expenditure and metabolic rates in over 4,000 adults from 34 nations—including both developed countries like the US and lower-income regions where physically demanding lifestyles prevail—the study found that people everywhere burn nearly the same number of calories daily, regardless of how active their routines are. Whether an individual was an American office worker or a hunter-gatherer from an African savannah, total energy expenditure remained surprisingly consistent.
One of the study’s lead authors, a professor of evolutionary anthropology, emphasized that the team used “doubly labeled water” metabolic studies—a gold standard technique in nutritional science—to get precise measurements of daily calorie use. This robust dataset allowed the researchers to confidently overturn assumptions that physical inactivity alone is driving the obesity crisis. “Increased energy intake has been roughly 10 times more important than declining total energy expenditure in driving the modern obesity crisis,” the authors wrote.
Expert voices have quickly rallied around the study’s findings. According to a professor at the Gillings School of Global Public Health at the University of North Carolina at Chapel Hill, who was quoted in the Washington Post, “This study confirms what I’ve been saying, which is that diet is the key culprit in our current [obesity] epidemic.” Another leading figure, director of the Food is Medicine Institute at Tufts University in Boston, remarked, “It’s clear from this important new research and other studies that changes to our food, not our activity, are the dominant drivers of obesity.”
Despite these results, the authors stress that the value of exercise should not be dismissed. Regular physical activity remains a keystone of good health, reducing the risk of cancer, cardiovascular disease, and many mental health conditions. What is shifting, however, is the role exercise plays in addressing the obesity epidemic. Instead of focusing primarily on physical activity, the authors argue, “public health efforts need to focus on diet,” especially ultra-processed foods, which increasingly dominate modern grocery aisles.
For Thailand, where obesity rates have doubled over the past decade and ultra-processed food consumption is sharply rising—especially among children and young adults—these findings have significant implications. Local data from the Ministry of Public Health shows that more than one in three Thai adults is now overweight, with childhood obesity emerging as a national concern [Ministry of Public Health, Thailand, 2024]. The Thai food landscape, shaped by traditions of fresh markets but increasingly influenced by fast food, sweetened beverages, and high-calorie processed snacks, mirrors global trends identified in the research.
Culturally, Thailand has long prided itself on a diverse local cuisine, marked by fresh produce, lean proteins, and herbal seasonings. But as convenience foods and sugary drinks have become more popular, the national diet has shifted away from its traditional roots. Nutrition experts in Thailand warn that while urban lifestyles have reduced physical activity to some extent, it is the quietly rising caloric intake—from restaurant portions, delivery apps, and imported snacks—that is doing more to expand waistlines.
Reflecting on regional disparities, health officials in Thailand highlight how urbanization and Westernization of diets are leading to greater consumption of processed foods, while rural populations still draw primarily from home-cooked, plant-based meals. Yet, as economic growth spreads, so too does the temptation of inexpensive, high-calorie foods.
Internationally, this study is likely to trigger fresh debate over policy responses at every level—from schools and offices to national governments. Should programs focus more on nutrition education, front-of-package food labeling, or even taxes on sugar and processed foods? Recent campaigns by the Thai government—such as the “Less Sweet, More Health” initiative and stricter advertising restrictions on children’s snacks—may be more vital than ever according to these new scientific insights.
Looking forward, experts say the fight against obesity must reckon with modern food environments rather than simply urging people to “move more.” As the study’s senior author pointed out, “This study doesn’t change the fact that exercise is essential for health. But if we want to reverse obesity trends, we must focus squarely on what’s on our plates.”
For Thai families, practical actions mean returning to local fresh food markets, emphasizing home cooking, and reducing reliance on processed snacks and sugary drinks—especially for children. For schools and policymakers, the challenge lies in making healthy food choices accessible, affordable, and appealing.
All sources referenced can be found at The Independent, the academic publishing platform PNAS, and statements from the World Health Organization.