A sweeping international study published this week in the Proceedings of the National Academy of Sciences (PNAS) is challenging one of the most entrenched beliefs about obesity: that sedentary lifestyles in wealthy nations are the main culprit behind rising rates of overweight and obesity. Instead, the study points a much sharper spotlight at diet—specifically, the prevalence of ultra-processed foods—as the major driver of the global obesity crisis. As Thailand and other middle-income nations grapple with rising rates of obesity, these findings hold urgent implications for public health policies, education campaigns, and everyday choices at the dining table.
At the heart of this landmark research is a comprehensive analysis of calorie expenditure data collected from over 4,000 adults living in 34 distinctly different cultural environments, ranging from the Hadza hunter-gatherers of Tanzania and forager-farmers in Bolivia to city-dwellers in the United States and executives in Norway. Using the gold-standard “doubly labeled water” method, researchers were able to precisely measure how many calories participants burned each day through both basic bodily functions and physical activity. This rigorous approach allowed for apples-to-apples comparisons across people of varying lifestyles, body sizes, and socioeconomic backgrounds. Contrary to widely held assumptions, the study found that people living in highly industrialized societies—including Americans and Europeans—burned about the same number of calories daily as individuals in subsistence farming or hunter-gatherer communities, once differences in body size were accounted for (washingtonpost.com).
In other words, the image of office workers and city residents as fundamentally more sedentary, and thereby less metabolically active, does not explain why obesity is so much more prevalent in wealthier countries. According to one of the study’s lead investigators, a professor of evolutionary anthropology and global health at Duke University, “inactivity is not the main cause of obesity in developed nations.” In fact, the study proposes a new theory referred to as the “constrained total energy expenditure model,” where our brains and bodies keep total energy output in a relatively narrow, regulated band—regardless of lifestyle. If someone burns more calories through strenuous activity, their body compensates by scaling down energy devoted to other processes, such as growth or reproduction, resulting in a surprisingly stable overall daily energy burn.
This concept flies in the face of decades of public health messaging that has largely placed the blame for obesity on increasingly sedentary lifestyles amid rapid urbanization and technological change. Yet if activity levels are not so different across the globe, what does set wealthy nations apart? The research points to two interlinked dietary factors: caloric overconsumption and the rise of ultra-processed foods. In a sub-analysis examining dietary patterns, the investigators found that a higher proportion of ultra-processed foods—defined as industrial formulations made from five or more ingredients—was strongly correlated with increased body-fat percentages across multiple populations.
“We’re eating too much, and probably eating too much of the wrong foods,” the Duke University scientist explained. In fact, the study estimated that excess calorie intake was approximately 10 times more influential than decreased physical activity in fueling the contemporary obesity crisis.
The implications for Thailand are profound. Over the past two decades, Thailand has seen a steady jump in overweight and obesity rates, especially in Bangkok and other major cities, mirroring patterns long observed in Western countries (source: WHO Thailand). According to figures from Thailand’s National Health Examination Survey, the prevalence of overweight and obesity among adults has climbed from approximately 16% in the early 1990s to over 32% today (MOPH, Thailand). The trend is particularly striking among children and adolescents, raising concerns about future burdens of diabetes, cardiovascular disease, and certain cancers.
A senior official from Thailand’s Department of Health acknowledged that urban dietary transitions—driven by the rapid expansion of supermarkets, fast food chains, and convenience stores—has led to wider adoption of ready-to-eat meals, sugary drinks, and snacks loaded with industrial additives. “What we see in school cafeterias and even at home is a sharp increase in ultra-processed food consumption, which this new research identifies as a key risk factor for obesity,” the official observed. Indeed, globally, studies have found that as much as 60% of caloric intake in some high-income countries comes from ultra-processed foods (BMJ Open), a pattern now increasingly echoed in Asia.
While the study’s conclusions shift much of the public health focus onto diet, the authors are careful not to diminish the vital role of exercise for other aspects of health, such as mental well-being, cardiovascular function, and prevention of metabolic disorders. “Exercise is essential for health. This study doesn’t change that,” the Duke researcher emphasized. Nevertheless, the practical takeaway for combating obesity is clear: reducing overall energy intake, and especially limiting ultra-processed foods, should be at the forefront of both individual choices and national strategies.
Key figures in the nutritional sciences community have endorsed the study’s findings. A professor at the Gillings School of Global Public Health at the University of North Carolina, a renowned authority on obesity, remarked, “Diet is the key culprit in our current epidemic—this is a well-done study.” The director of the Food is Medicine Institute at Tufts University further noted, “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.”
The relevance of this new understanding extends well beyond diet fads or weight-loss products. Historical and cultural factors play a decisive role in shaping food environments and dietary habits. In much of rural Thailand, traditional diets have long centered around rice, fresh fruits, vegetables, and locally sourced proteins—foods that are minimally processed and nutrient-dense. However, as urbanization accelerates and Western-style supermarkets proliferate, patterns of consumption have shifted toward convenience and flavor intensity, often at the expense of nutrition and satiety. This “nutrition transition” is a global phenomenon, but it is especially pronounced in countries experiencing rapid economic growth (The Lancet Global Health).
Thailand’s public health officials are already pushing for policy changes in response. The Ministry of Public Health continues to campaign against sugary beverages and has implemented front-of-pack labeling to signal high sodium, fat, or sugar content on packaged goods. Experts from the Thai Health Promotion Foundation have urged stricter regulation of food advertising to children and wider availability of healthy foods in schools and public canteens. “We need a concerted effort involving parents, teachers, food retailers, and policymakers,” said a representative from the foundation. “Education is critical, but structural measures to make healthy choices easier and more affordable are just as important.”
Looking forward, scientists warn that the global diffusion of ultra-processed food will only accelerate as food systems become more integrated and globalized. This means that obesity—and associated health risks—could become the norm rather than the exception, unless societies act decisively. Researchers are calling for renewed investments in nutrition literacy, community health outreach, and improved access to fresh, affordable whole foods.
So, what can Thai readers do today? First, try to minimize ultra-processed foods in the diet: check ingredients lists for long, unfamiliar names and opt for meals prepared from scratch with vegetables, rice, fish, eggs, and fruit. Limit the frequency of sugary snack and beverage consumption, and remember that refocusing on traditional Thai dietary patterns can offer both enjoyment and health. For families, rethink “convenience”—even quick stir-fried or boiled dishes can be made rapidly without resorting to ultraprocessed sauces and packet foods. And for policymakers, consider this a clarion call to redouble efforts in food system regulation, school meal standards, and public health education.
The new research makes clear that, while exercise remains vital, what matters most for obesity prevention and treatment is what—and how much—we eat. Returning to Thai culinary roots, emphasizing whole foods, and being mindful about global dietary shifts can help turn the tide, benefiting both individuals and society as a whole.
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